diff --git a/src/profiler/sampler.cc b/src/profiler/sampler.cc
new file mode 100644
index 0000000..dc4c4c4
--- /dev/null
+++ b/src/profiler/sampler.cc
@@ -0,0 +1,861 @@
+// Copyright 2013 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "src/profiler/sampler.h"
+
+#if V8_OS_POSIX && !V8_OS_CYGWIN
+
+#define USE_SIGNALS
+
+#include <errno.h>
+#include <pthread.h>
+#include <signal.h>
+#include <sys/time.h>
+
+#if !V8_OS_QNX && !V8_OS_NACL && !V8_OS_AIX
+#include <sys/syscall.h>  // NOLINT
+#endif
+
+#if V8_OS_MACOSX
+#include <mach/mach.h>
+// OpenBSD doesn't have <ucontext.h>. ucontext_t lives in <signal.h>
+// and is a typedef for struct sigcontext. There is no uc_mcontext.
+#elif(!V8_OS_ANDROID || defined(__BIONIC_HAVE_UCONTEXT_T)) && \
+    !V8_OS_OPENBSD && !V8_OS_NACL
+#include <ucontext.h>
+#endif
+
+#include <unistd.h>
+
+// GLibc on ARM defines mcontext_t has a typedef for 'struct sigcontext'.
+// Old versions of the C library <signal.h> didn't define the type.
+#if V8_OS_ANDROID && !defined(__BIONIC_HAVE_UCONTEXT_T) && \
+    (defined(__arm__) || defined(__aarch64__)) && \
+    !defined(__BIONIC_HAVE_STRUCT_SIGCONTEXT)
+#include <asm/sigcontext.h>  // NOLINT
+#endif
+
+#elif V8_OS_WIN || V8_OS_CYGWIN
+
+#include "src/base/win32-headers.h"
+
+#endif
+
+#include "src/base/platform/platform.h"
+#include "src/flags.h"
+#include "src/frames-inl.h"
+#include "src/log.h"
+#include "src/profiler/cpu-profiler-inl.h"
+#include "src/simulator.h"
+#include "src/v8threads.h"
+#include "src/vm-state-inl.h"
+
+
+#if V8_OS_ANDROID && !defined(__BIONIC_HAVE_UCONTEXT_T)
+
+// Not all versions of Android's C library provide ucontext_t.
+// Detect this and provide custom but compatible definitions. Note that these
+// follow the GLibc naming convention to access register values from
+// mcontext_t.
+//
+// See http://code.google.com/p/android/issues/detail?id=34784
+
+#if defined(__arm__)
+
+typedef struct sigcontext mcontext_t;
+
+typedef struct ucontext {
+  uint32_t uc_flags;
+  struct ucontext* uc_link;
+  stack_t uc_stack;
+  mcontext_t uc_mcontext;
+  // Other fields are not used by V8, don't define them here.
+} ucontext_t;
+
+#elif defined(__aarch64__)
+
+typedef struct sigcontext mcontext_t;
+
+typedef struct ucontext {
+  uint64_t uc_flags;
+  struct ucontext *uc_link;
+  stack_t uc_stack;
+  mcontext_t uc_mcontext;
+  // Other fields are not used by V8, don't define them here.
+} ucontext_t;
+
+#elif defined(__mips__)
+// MIPS version of sigcontext, for Android bionic.
+typedef struct {
+  uint32_t regmask;
+  uint32_t status;
+  uint64_t pc;
+  uint64_t gregs[32];
+  uint64_t fpregs[32];
+  uint32_t acx;
+  uint32_t fpc_csr;
+  uint32_t fpc_eir;
+  uint32_t used_math;
+  uint32_t dsp;
+  uint64_t mdhi;
+  uint64_t mdlo;
+  uint32_t hi1;
+  uint32_t lo1;
+  uint32_t hi2;
+  uint32_t lo2;
+  uint32_t hi3;
+  uint32_t lo3;
+} mcontext_t;
+
+typedef struct ucontext {
+  uint32_t uc_flags;
+  struct ucontext* uc_link;
+  stack_t uc_stack;
+  mcontext_t uc_mcontext;
+  // Other fields are not used by V8, don't define them here.
+} ucontext_t;
+
+#elif defined(__i386__)
+// x86 version for Android.
+typedef struct {
+  uint32_t gregs[19];
+  void* fpregs;
+  uint32_t oldmask;
+  uint32_t cr2;
+} mcontext_t;
+
+typedef uint32_t kernel_sigset_t[2];  // x86 kernel uses 64-bit signal masks
+typedef struct ucontext {
+  uint32_t uc_flags;
+  struct ucontext* uc_link;
+  stack_t uc_stack;
+  mcontext_t uc_mcontext;
+  // Other fields are not used by V8, don't define them here.
+} ucontext_t;
+enum { REG_EBP = 6, REG_ESP = 7, REG_EIP = 14 };
+
+#elif defined(__x86_64__)
+// x64 version for Android.
+typedef struct {
+  uint64_t gregs[23];
+  void* fpregs;
+  uint64_t __reserved1[8];
+} mcontext_t;
+
+typedef struct ucontext {
+  uint64_t uc_flags;
+  struct ucontext *uc_link;
+  stack_t uc_stack;
+  mcontext_t uc_mcontext;
+  // Other fields are not used by V8, don't define them here.
+} ucontext_t;
+enum { REG_RBP = 10, REG_RSP = 15, REG_RIP = 16 };
+#endif
+
+#endif  // V8_OS_ANDROID && !defined(__BIONIC_HAVE_UCONTEXT_T)
+
+
+namespace v8 {
+namespace internal {
+
+namespace {
+
+class PlatformDataCommon : public Malloced {
+ public:
+  PlatformDataCommon() : profiled_thread_id_(ThreadId::Current()) {}
+  ThreadId profiled_thread_id() { return profiled_thread_id_; }
+
+ protected:
+  ~PlatformDataCommon() {}
+
+ private:
+  ThreadId profiled_thread_id_;
+};
+
+
+bool IsSamePage(byte* ptr1, byte* ptr2) {
+  const uint32_t kPageSize = 4096;
+  uintptr_t mask = ~static_cast<uintptr_t>(kPageSize - 1);
+  return (reinterpret_cast<uintptr_t>(ptr1) & mask) ==
+         (reinterpret_cast<uintptr_t>(ptr2) & mask);
+}
+
+
+// Check if the code at specified address could potentially be a
+// frame setup code.
+bool IsNoFrameRegion(Address address) {
+  struct Pattern {
+    int bytes_count;
+    byte bytes[8];
+    int offsets[4];
+  };
+  byte* pc = reinterpret_cast<byte*>(address);
+  static Pattern patterns[] = {
+#if V8_HOST_ARCH_IA32
+    // push %ebp
+    // mov %esp,%ebp
+    {3, {0x55, 0x89, 0xe5}, {0, 1, -1}},
+    // pop %ebp
+    // ret N
+    {2, {0x5d, 0xc2}, {0, 1, -1}},
+    // pop %ebp
+    // ret
+    {2, {0x5d, 0xc3}, {0, 1, -1}},
+#elif V8_HOST_ARCH_X64
+    // pushq %rbp
+    // movq %rsp,%rbp
+    {4, {0x55, 0x48, 0x89, 0xe5}, {0, 1, -1}},
+    // popq %rbp
+    // ret N
+    {2, {0x5d, 0xc2}, {0, 1, -1}},
+    // popq %rbp
+    // ret
+    {2, {0x5d, 0xc3}, {0, 1, -1}},
+#endif
+    {0, {}, {}}
+  };
+  for (Pattern* pattern = patterns; pattern->bytes_count; ++pattern) {
+    for (int* offset_ptr = pattern->offsets; *offset_ptr != -1; ++offset_ptr) {
+      int offset = *offset_ptr;
+      if (!offset || IsSamePage(pc, pc - offset)) {
+        MSAN_MEMORY_IS_INITIALIZED(pc - offset, pattern->bytes_count);
+        if (!memcmp(pc - offset, pattern->bytes, pattern->bytes_count))
+          return true;
+      } else {
+        // It is not safe to examine bytes on another page as it might not be
+        // allocated thus causing a SEGFAULT.
+        // Check the pattern part that's on the same page and
+        // pessimistically assume it could be the entire pattern match.
+        MSAN_MEMORY_IS_INITIALIZED(pc, pattern->bytes_count - offset);
+        if (!memcmp(pc, pattern->bytes + offset, pattern->bytes_count - offset))
+          return true;
+      }
+    }
+  }
+  return false;
+}
+
+}  // namespace
+
+#if defined(USE_SIGNALS)
+
+class Sampler::PlatformData : public PlatformDataCommon {
+ public:
+  PlatformData() : vm_tid_(pthread_self()) {}
+  pthread_t vm_tid() const { return vm_tid_; }
+
+ private:
+  pthread_t vm_tid_;
+};
+
+#elif V8_OS_WIN || V8_OS_CYGWIN
+
+// ----------------------------------------------------------------------------
+// Win32 profiler support. On Cygwin we use the same sampler implementation as
+// on Win32.
+
+class Sampler::PlatformData : public PlatformDataCommon {
+ public:
+  // Get a handle to the calling thread. This is the thread that we are
+  // going to profile. We need to make a copy of the handle because we are
+  // going to use it in the sampler thread. Using GetThreadHandle() will
+  // not work in this case. We're using OpenThread because DuplicateHandle
+  // for some reason doesn't work in Chrome's sandbox.
+  PlatformData()
+      : profiled_thread_(OpenThread(THREAD_GET_CONTEXT |
+                                    THREAD_SUSPEND_RESUME |
+                                    THREAD_QUERY_INFORMATION,
+                                    false,
+                                    GetCurrentThreadId())) {}
+
+  ~PlatformData() {
+    if (profiled_thread_ != NULL) {
+      CloseHandle(profiled_thread_);
+      profiled_thread_ = NULL;
+    }
+  }
+
+  HANDLE profiled_thread() { return profiled_thread_; }
+
+ private:
+  HANDLE profiled_thread_;
+};
+#endif
+
+
+#if defined(USE_SIMULATOR)
+class SimulatorHelper {
+ public:
+  inline bool Init(Isolate* isolate) {
+    simulator_ = isolate->thread_local_top()->simulator_;
+    // Check if there is active simulator.
+    return simulator_ != NULL;
+  }
+
+  inline void FillRegisters(v8::RegisterState* state) {
+#if V8_TARGET_ARCH_ARM
+    if (!simulator_->has_bad_pc()) {
+      state->pc = reinterpret_cast<Address>(simulator_->get_pc());
+    }
+    state->sp = reinterpret_cast<Address>(simulator_->get_register(
+        Simulator::sp));
+    state->fp = reinterpret_cast<Address>(simulator_->get_register(
+        Simulator::r11));
+#elif V8_TARGET_ARCH_ARM64
+    if (simulator_->sp() == 0 || simulator_->fp() == 0) {
+      // It's possible that the simulator is interrupted while it is updating
+      // the sp or fp register. ARM64 simulator does this in two steps:
+      // first setting it to zero and then setting it to a new value.
+      // Bailout if sp/fp doesn't contain the new value.
+      //
+      // FIXME: The above doesn't really solve the issue.
+      // If a 64-bit target is executed on a 32-bit host even the final
+      // write is non-atomic, so it might obtain a half of the result.
+      // Moreover as long as the register set code uses memcpy (as of now),
+      // it is not guaranteed to be atomic even when both host and target
+      // are of same bitness.
+      return;
+    }
+    state->pc = reinterpret_cast<Address>(simulator_->pc());
+    state->sp = reinterpret_cast<Address>(simulator_->sp());
+    state->fp = reinterpret_cast<Address>(simulator_->fp());
+#elif V8_TARGET_ARCH_MIPS || V8_TARGET_ARCH_MIPS64
+    if (!simulator_->has_bad_pc()) {
+      state->pc = reinterpret_cast<Address>(simulator_->get_pc());
+    }
+    state->sp = reinterpret_cast<Address>(simulator_->get_register(
+        Simulator::sp));
+    state->fp = reinterpret_cast<Address>(simulator_->get_register(
+        Simulator::fp));
+#elif V8_TARGET_ARCH_PPC
+    if (!simulator_->has_bad_pc()) {
+      state->pc = reinterpret_cast<Address>(simulator_->get_pc());
+    }
+    state->sp =
+        reinterpret_cast<Address>(simulator_->get_register(Simulator::sp));
+    state->fp =
+        reinterpret_cast<Address>(simulator_->get_register(Simulator::fp));
+#endif
+  }
+
+ private:
+  Simulator* simulator_;
+};
+#endif  // USE_SIMULATOR
+
+
+#if defined(USE_SIGNALS)
+
+class SignalHandler : public AllStatic {
+ public:
+  static void SetUp() { if (!mutex_) mutex_ = new base::Mutex(); }
+  static void TearDown() { delete mutex_; mutex_ = NULL; }
+
+  static void IncreaseSamplerCount() {
+    base::LockGuard<base::Mutex> lock_guard(mutex_);
+    if (++client_count_ == 1) Install();
+  }
+
+  static void DecreaseSamplerCount() {
+    base::LockGuard<base::Mutex> lock_guard(mutex_);
+    if (--client_count_ == 0) Restore();
+  }
+
+  static bool Installed() {
+    return signal_handler_installed_;
+  }
+
+ private:
+  static void Install() {
+#if !V8_OS_NACL
+    struct sigaction sa;
+    sa.sa_sigaction = &HandleProfilerSignal;
+    sigemptyset(&sa.sa_mask);
+#if V8_OS_QNX
+    sa.sa_flags = SA_SIGINFO;
+#else
+    sa.sa_flags = SA_RESTART | SA_SIGINFO;
+#endif
+    signal_handler_installed_ =
+        (sigaction(SIGPROF, &sa, &old_signal_handler_) == 0);
+#endif
+  }
+
+  static void Restore() {
+#if !V8_OS_NACL
+    if (signal_handler_installed_) {
+      sigaction(SIGPROF, &old_signal_handler_, 0);
+      signal_handler_installed_ = false;
+    }
+#endif
+  }
+
+#if !V8_OS_NACL
+  static void HandleProfilerSignal(int signal, siginfo_t* info, void* context);
+#endif
+  // Protects the process wide state below.
+  static base::Mutex* mutex_;
+  static int client_count_;
+  static bool signal_handler_installed_;
+  static struct sigaction old_signal_handler_;
+};
+
+
+base::Mutex* SignalHandler::mutex_ = NULL;
+int SignalHandler::client_count_ = 0;
+struct sigaction SignalHandler::old_signal_handler_;
+bool SignalHandler::signal_handler_installed_ = false;
+
+
+// As Native Client does not support signal handling, profiling is disabled.
+#if !V8_OS_NACL
+void SignalHandler::HandleProfilerSignal(int signal, siginfo_t* info,
+                                         void* context) {
+  USE(info);
+  if (signal != SIGPROF) return;
+  Isolate* isolate = Isolate::UnsafeCurrent();
+  if (isolate == NULL || !isolate->IsInUse()) {
+    // We require a fully initialized and entered isolate.
+    return;
+  }
+  if (v8::Locker::IsActive() &&
+      !isolate->thread_manager()->IsLockedByCurrentThread()) {
+    return;
+  }
+
+  Sampler* sampler = isolate->logger()->sampler();
+  if (sampler == NULL) return;
+
+  v8::RegisterState state;
+
+#if defined(USE_SIMULATOR)
+  SimulatorHelper helper;
+  if (!helper.Init(isolate)) return;
+  helper.FillRegisters(&state);
+  // It possible that the simulator is interrupted while it is updating
+  // the sp or fp register. ARM64 simulator does this in two steps:
+  // first setting it to zero and then setting it to the new value.
+  // Bailout if sp/fp doesn't contain the new value.
+  if (state.sp == 0 || state.fp == 0) return;
+#else
+  // Extracting the sample from the context is extremely machine dependent.
+  ucontext_t* ucontext = reinterpret_cast<ucontext_t*>(context);
+#if !(V8_OS_OPENBSD || (V8_OS_LINUX && V8_HOST_ARCH_PPC))
+  mcontext_t& mcontext = ucontext->uc_mcontext;
+#endif
+#if V8_OS_LINUX
+#if V8_HOST_ARCH_IA32
+  state.pc = reinterpret_cast<Address>(mcontext.gregs[REG_EIP]);
+  state.sp = reinterpret_cast<Address>(mcontext.gregs[REG_ESP]);
+  state.fp = reinterpret_cast<Address>(mcontext.gregs[REG_EBP]);
+#elif V8_HOST_ARCH_X64
+  state.pc = reinterpret_cast<Address>(mcontext.gregs[REG_RIP]);
+  state.sp = reinterpret_cast<Address>(mcontext.gregs[REG_RSP]);
+  state.fp = reinterpret_cast<Address>(mcontext.gregs[REG_RBP]);
+#elif V8_HOST_ARCH_ARM
+#if V8_LIBC_GLIBC && !V8_GLIBC_PREREQ(2, 4)
+  // Old GLibc ARM versions used a gregs[] array to access the register
+  // values from mcontext_t.
+  state.pc = reinterpret_cast<Address>(mcontext.gregs[R15]);
+  state.sp = reinterpret_cast<Address>(mcontext.gregs[R13]);
+  state.fp = reinterpret_cast<Address>(mcontext.gregs[R11]);
+#else
+  state.pc = reinterpret_cast<Address>(mcontext.arm_pc);
+  state.sp = reinterpret_cast<Address>(mcontext.arm_sp);
+  state.fp = reinterpret_cast<Address>(mcontext.arm_fp);
+#endif  // V8_LIBC_GLIBC && !V8_GLIBC_PREREQ(2, 4)
+#elif V8_HOST_ARCH_ARM64
+  state.pc = reinterpret_cast<Address>(mcontext.pc);
+  state.sp = reinterpret_cast<Address>(mcontext.sp);
+  // FP is an alias for x29.
+  state.fp = reinterpret_cast<Address>(mcontext.regs[29]);
+#elif V8_HOST_ARCH_MIPS
+  state.pc = reinterpret_cast<Address>(mcontext.pc);
+  state.sp = reinterpret_cast<Address>(mcontext.gregs[29]);
+  state.fp = reinterpret_cast<Address>(mcontext.gregs[30]);
+#elif V8_HOST_ARCH_MIPS64
+  state.pc = reinterpret_cast<Address>(mcontext.pc);
+  state.sp = reinterpret_cast<Address>(mcontext.gregs[29]);
+  state.fp = reinterpret_cast<Address>(mcontext.gregs[30]);
+#elif V8_HOST_ARCH_PPC
+  state.pc = reinterpret_cast<Address>(ucontext->uc_mcontext.regs->nip);
+  state.sp = reinterpret_cast<Address>(ucontext->uc_mcontext.regs->gpr[PT_R1]);
+  state.fp = reinterpret_cast<Address>(ucontext->uc_mcontext.regs->gpr[PT_R31]);
+#endif  // V8_HOST_ARCH_*
+#elif V8_OS_MACOSX
+#if V8_HOST_ARCH_X64
+#if __DARWIN_UNIX03
+  state.pc = reinterpret_cast<Address>(mcontext->__ss.__rip);
+  state.sp = reinterpret_cast<Address>(mcontext->__ss.__rsp);
+  state.fp = reinterpret_cast<Address>(mcontext->__ss.__rbp);
+#else  // !__DARWIN_UNIX03
+  state.pc = reinterpret_cast<Address>(mcontext->ss.rip);
+  state.sp = reinterpret_cast<Address>(mcontext->ss.rsp);
+  state.fp = reinterpret_cast<Address>(mcontext->ss.rbp);
+#endif  // __DARWIN_UNIX03
+#elif V8_HOST_ARCH_IA32
+#if __DARWIN_UNIX03
+  state.pc = reinterpret_cast<Address>(mcontext->__ss.__eip);
+  state.sp = reinterpret_cast<Address>(mcontext->__ss.__esp);
+  state.fp = reinterpret_cast<Address>(mcontext->__ss.__ebp);
+#else  // !__DARWIN_UNIX03
+  state.pc = reinterpret_cast<Address>(mcontext->ss.eip);
+  state.sp = reinterpret_cast<Address>(mcontext->ss.esp);
+  state.fp = reinterpret_cast<Address>(mcontext->ss.ebp);
+#endif  // __DARWIN_UNIX03
+#endif  // V8_HOST_ARCH_IA32
+#elif V8_OS_FREEBSD
+#if V8_HOST_ARCH_IA32
+  state.pc = reinterpret_cast<Address>(mcontext.mc_eip);
+  state.sp = reinterpret_cast<Address>(mcontext.mc_esp);
+  state.fp = reinterpret_cast<Address>(mcontext.mc_ebp);
+#elif V8_HOST_ARCH_X64
+  state.pc = reinterpret_cast<Address>(mcontext.mc_rip);
+  state.sp = reinterpret_cast<Address>(mcontext.mc_rsp);
+  state.fp = reinterpret_cast<Address>(mcontext.mc_rbp);
+#elif V8_HOST_ARCH_ARM
+  state.pc = reinterpret_cast<Address>(mcontext.mc_r15);
+  state.sp = reinterpret_cast<Address>(mcontext.mc_r13);
+  state.fp = reinterpret_cast<Address>(mcontext.mc_r11);
+#endif  // V8_HOST_ARCH_*
+#elif V8_OS_NETBSD
+#if V8_HOST_ARCH_IA32
+  state.pc = reinterpret_cast<Address>(mcontext.__gregs[_REG_EIP]);
+  state.sp = reinterpret_cast<Address>(mcontext.__gregs[_REG_ESP]);
+  state.fp = reinterpret_cast<Address>(mcontext.__gregs[_REG_EBP]);
+#elif V8_HOST_ARCH_X64
+  state.pc = reinterpret_cast<Address>(mcontext.__gregs[_REG_RIP]);
+  state.sp = reinterpret_cast<Address>(mcontext.__gregs[_REG_RSP]);
+  state.fp = reinterpret_cast<Address>(mcontext.__gregs[_REG_RBP]);
+#endif  // V8_HOST_ARCH_*
+#elif V8_OS_OPENBSD
+#if V8_HOST_ARCH_IA32
+  state.pc = reinterpret_cast<Address>(ucontext->sc_eip);
+  state.sp = reinterpret_cast<Address>(ucontext->sc_esp);
+  state.fp = reinterpret_cast<Address>(ucontext->sc_ebp);
+#elif V8_HOST_ARCH_X64
+  state.pc = reinterpret_cast<Address>(ucontext->sc_rip);
+  state.sp = reinterpret_cast<Address>(ucontext->sc_rsp);
+  state.fp = reinterpret_cast<Address>(ucontext->sc_rbp);
+#endif  // V8_HOST_ARCH_*
+#elif V8_OS_SOLARIS
+  state.pc = reinterpret_cast<Address>(mcontext.gregs[REG_PC]);
+  state.sp = reinterpret_cast<Address>(mcontext.gregs[REG_SP]);
+  state.fp = reinterpret_cast<Address>(mcontext.gregs[REG_FP]);
+#elif V8_OS_QNX
+#if V8_HOST_ARCH_IA32
+  state.pc = reinterpret_cast<Address>(mcontext.cpu.eip);
+  state.sp = reinterpret_cast<Address>(mcontext.cpu.esp);
+  state.fp = reinterpret_cast<Address>(mcontext.cpu.ebp);
+#elif V8_HOST_ARCH_ARM
+  state.pc = reinterpret_cast<Address>(mcontext.cpu.gpr[ARM_REG_PC]);
+  state.sp = reinterpret_cast<Address>(mcontext.cpu.gpr[ARM_REG_SP]);
+  state.fp = reinterpret_cast<Address>(mcontext.cpu.gpr[ARM_REG_FP]);
+#endif  // V8_HOST_ARCH_*
+#elif V8_OS_AIX
+  state.pc = reinterpret_cast<Address>(mcontext.jmp_context.iar);
+  state.sp = reinterpret_cast<Address>(mcontext.jmp_context.gpr[1]);
+  state.fp = reinterpret_cast<Address>(mcontext.jmp_context.gpr[31]);
+#endif  // V8_OS_AIX
+#endif  // USE_SIMULATOR
+  sampler->SampleStack(state);
+}
+#endif  // V8_OS_NACL
+
+#endif
+
+
+class SamplerThread : public base::Thread {
+ public:
+  static const int kSamplerThreadStackSize = 64 * KB;
+
+  explicit SamplerThread(int interval)
+      : Thread(base::Thread::Options("SamplerThread", kSamplerThreadStackSize)),
+        interval_(interval) {}
+
+  static void SetUp() { if (!mutex_) mutex_ = new base::Mutex(); }
+  static void TearDown() { delete mutex_; mutex_ = NULL; }
+
+  static void AddActiveSampler(Sampler* sampler) {
+    bool need_to_start = false;
+    base::LockGuard<base::Mutex> lock_guard(mutex_);
+    if (instance_ == NULL) {
+      // Start a thread that will send SIGPROF signal to VM threads,
+      // when CPU profiling will be enabled.
+      instance_ = new SamplerThread(sampler->interval());
+      need_to_start = true;
+    }
+
+    DCHECK(sampler->IsActive());
+    DCHECK(!instance_->active_samplers_.Contains(sampler));
+    DCHECK(instance_->interval_ == sampler->interval());
+    instance_->active_samplers_.Add(sampler);
+
+    if (need_to_start) instance_->StartSynchronously();
+  }
+
+  static void RemoveActiveSampler(Sampler* sampler) {
+    SamplerThread* instance_to_remove = NULL;
+    {
+      base::LockGuard<base::Mutex> lock_guard(mutex_);
+
+      DCHECK(sampler->IsActive());
+      bool removed = instance_->active_samplers_.RemoveElement(sampler);
+      DCHECK(removed);
+      USE(removed);
+
+      // We cannot delete the instance immediately as we need to Join() the
+      // thread but we are holding mutex_ and the thread may try to acquire it.
+      if (instance_->active_samplers_.is_empty()) {
+        instance_to_remove = instance_;
+        instance_ = NULL;
+      }
+    }
+
+    if (!instance_to_remove) return;
+    instance_to_remove->Join();
+    delete instance_to_remove;
+  }
+
+  // Implement Thread::Run().
+  virtual void Run() {
+    while (true) {
+      {
+        base::LockGuard<base::Mutex> lock_guard(mutex_);
+        if (active_samplers_.is_empty()) break;
+        // When CPU profiling is enabled both JavaScript and C++ code is
+        // profiled. We must not suspend.
+        for (int i = 0; i < active_samplers_.length(); ++i) {
+          Sampler* sampler = active_samplers_.at(i);
+          if (!sampler->IsProfiling()) continue;
+          sampler->DoSample();
+        }
+      }
+      base::OS::Sleep(base::TimeDelta::FromMilliseconds(interval_));
+    }
+  }
+
+ private:
+  // Protects the process wide state below.
+  static base::Mutex* mutex_;
+  static SamplerThread* instance_;
+
+  const int interval_;
+  List<Sampler*> active_samplers_;
+
+  DISALLOW_COPY_AND_ASSIGN(SamplerThread);
+};
+
+
+base::Mutex* SamplerThread::mutex_ = NULL;
+SamplerThread* SamplerThread::instance_ = NULL;
+
+
+//
+// StackTracer implementation
+//
+DISABLE_ASAN void TickSample::Init(Isolate* isolate,
+                                   const v8::RegisterState& regs,
+                                   RecordCEntryFrame record_c_entry_frame) {
+  timestamp = base::TimeTicks::HighResolutionNow();
+  pc = reinterpret_cast<Address>(regs.pc);
+  state = isolate->current_vm_state();
+
+  // Avoid collecting traces while doing GC.
+  if (state == GC) return;
+
+  Address js_entry_sp = isolate->js_entry_sp();
+  if (js_entry_sp == 0) return;  // Not executing JS now.
+
+  if (pc && IsNoFrameRegion(pc)) {
+    pc = 0;
+    return;
+  }
+
+  ExternalCallbackScope* scope = isolate->external_callback_scope();
+  Address handler = Isolate::handler(isolate->thread_local_top());
+  // If there is a handler on top of the external callback scope then
+  // we have already entrered JavaScript again and the external callback
+  // is not the top function.
+  if (scope && scope->scope_address() < handler) {
+    external_callback = scope->callback();
+    has_external_callback = true;
+  } else {
+    // sp register may point at an arbitrary place in memory, make
+    // sure MSAN doesn't complain about it.
+    MSAN_MEMORY_IS_INITIALIZED(regs.sp, sizeof(Address));
+    // Sample potential return address value for frameless invocation of
+    // stubs (we'll figure out later, if this value makes sense).
+    tos = Memory::Address_at(reinterpret_cast<Address>(regs.sp));
+    has_external_callback = false;
+  }
+
+  SafeStackFrameIterator it(isolate, reinterpret_cast<Address>(regs.fp),
+                            reinterpret_cast<Address>(regs.sp), js_entry_sp);
+  top_frame_type = it.top_frame_type();
+
+  SampleInfo info;
+  GetStackSample(isolate, regs, record_c_entry_frame,
+                 reinterpret_cast<void**>(&stack[0]), kMaxFramesCount, &info);
+  frames_count = static_cast<unsigned>(info.frames_count);
+}
+
+
+void TickSample::GetStackSample(Isolate* isolate, const v8::RegisterState& regs,
+                                RecordCEntryFrame record_c_entry_frame,
+                                void** frames, size_t frames_limit,
+                                v8::SampleInfo* sample_info) {
+  sample_info->frames_count = 0;
+  sample_info->vm_state = isolate->current_vm_state();
+  if (sample_info->vm_state == GC) return;
+
+  Address js_entry_sp = isolate->js_entry_sp();
+  if (js_entry_sp == 0) return;  // Not executing JS now.
+
+  SafeStackFrameIterator it(isolate, reinterpret_cast<Address>(regs.fp),
+                            reinterpret_cast<Address>(regs.sp), js_entry_sp);
+  size_t i = 0;
+  if (record_c_entry_frame == kIncludeCEntryFrame && !it.done() &&
+      it.top_frame_type() == StackFrame::EXIT) {
+    frames[i++] = isolate->c_function();
+  }
+  while (!it.done() && i < frames_limit) {
+    frames[i++] = it.frame()->pc();
+    it.Advance();
+  }
+  sample_info->frames_count = i;
+}
+
+
+void Sampler::SetUp() {
+#if defined(USE_SIGNALS)
+  SignalHandler::SetUp();
+#endif
+  SamplerThread::SetUp();
+}
+
+
+void Sampler::TearDown() {
+  SamplerThread::TearDown();
+#if defined(USE_SIGNALS)
+  SignalHandler::TearDown();
+#endif
+}
+
+
+Sampler::Sampler(Isolate* isolate, int interval)
+    : isolate_(isolate),
+      interval_(interval),
+      profiling_(false),
+      has_processing_thread_(false),
+      active_(false),
+      is_counting_samples_(false),
+      js_and_external_sample_count_(0) {
+  data_ = new PlatformData;
+}
+
+
+Sampler::~Sampler() {
+  DCHECK(!IsActive());
+  delete data_;
+}
+
+
+void Sampler::Start() {
+  DCHECK(!IsActive());
+  SetActive(true);
+  SamplerThread::AddActiveSampler(this);
+}
+
+
+void Sampler::Stop() {
+  DCHECK(IsActive());
+  SamplerThread::RemoveActiveSampler(this);
+  SetActive(false);
+}
+
+
+void Sampler::IncreaseProfilingDepth() {
+  base::NoBarrier_AtomicIncrement(&profiling_, 1);
+#if defined(USE_SIGNALS)
+  SignalHandler::IncreaseSamplerCount();
+#endif
+}
+
+
+void Sampler::DecreaseProfilingDepth() {
+#if defined(USE_SIGNALS)
+  SignalHandler::DecreaseSamplerCount();
+#endif
+  base::NoBarrier_AtomicIncrement(&profiling_, -1);
+}
+
+
+void Sampler::SampleStack(const v8::RegisterState& state) {
+  TickSample* sample = isolate_->cpu_profiler()->StartTickSample();
+  TickSample sample_obj;
+  if (sample == NULL) sample = &sample_obj;
+  sample->Init(isolate_, state, TickSample::kIncludeCEntryFrame);
+  if (is_counting_samples_) {
+    if (sample->state == JS || sample->state == EXTERNAL) {
+      ++js_and_external_sample_count_;
+    }
+  }
+  Tick(sample);
+  if (sample != &sample_obj) {
+    isolate_->cpu_profiler()->FinishTickSample();
+  }
+}
+
+
+#if defined(USE_SIGNALS)
+
+void Sampler::DoSample() {
+  if (!SignalHandler::Installed()) return;
+  pthread_kill(platform_data()->vm_tid(), SIGPROF);
+}
+
+#elif V8_OS_WIN || V8_OS_CYGWIN
+
+void Sampler::DoSample() {
+  HANDLE profiled_thread = platform_data()->profiled_thread();
+  if (profiled_thread == NULL) return;
+
+#if defined(USE_SIMULATOR)
+  SimulatorHelper helper;
+  if (!helper.Init(isolate())) return;
+#endif
+
+  const DWORD kSuspendFailed = static_cast<DWORD>(-1);
+  if (SuspendThread(profiled_thread) == kSuspendFailed) return;
+
+  // Context used for sampling the register state of the profiled thread.
+  CONTEXT context;
+  memset(&context, 0, sizeof(context));
+  context.ContextFlags = CONTEXT_FULL;
+  if (GetThreadContext(profiled_thread, &context) != 0) {
+    v8::RegisterState state;
+#if defined(USE_SIMULATOR)
+    helper.FillRegisters(&state);
+#else
+#if V8_HOST_ARCH_X64
+    state.pc = reinterpret_cast<Address>(context.Rip);
+    state.sp = reinterpret_cast<Address>(context.Rsp);
+    state.fp = reinterpret_cast<Address>(context.Rbp);
+#else
+    state.pc = reinterpret_cast<Address>(context.Eip);
+    state.sp = reinterpret_cast<Address>(context.Esp);
+    state.fp = reinterpret_cast<Address>(context.Ebp);
+#endif
+#endif  // USE_SIMULATOR
+    SampleStack(state);
+  }
+  ResumeThread(profiled_thread);
+}
+
+#endif  // USE_SIGNALS
+
+
+}  // namespace internal
+}  // namespace v8