Update V8 to r7427: Initial merge by git

As required by WebKit r82507

Change-Id: I7ae83ef3f689356043b4929255b7c1dd31d8c5df
diff --git a/src/debug-agent.h b/src/debug-agent.h
index 4cedb83..a25002e 100644
--- a/src/debug-agent.h
+++ b/src/debug-agent.h
@@ -43,18 +43,18 @@
 // handles connection from a remote debugger.
 class DebuggerAgent: public Thread {
  public:
-  explicit DebuggerAgent(const char* name, int port)
-      : Thread(name),
+  DebuggerAgent(Isolate* isolate, const char* name, int port)
+      : Thread(isolate, name),
         name_(StrDup(name)), port_(port),
         server_(OS::CreateSocket()), terminate_(false),
         session_access_(OS::CreateMutex()), session_(NULL),
         terminate_now_(OS::CreateSemaphore(0)),
         listening_(OS::CreateSemaphore(0)) {
-    ASSERT(instance_ == NULL);
-    instance_ = this;
+    ASSERT(Isolate::Current()->debugger_agent_instance() == NULL);
+    Isolate::Current()->set_debugger_agent_instance(this);
   }
   ~DebuggerAgent() {
-     instance_ = NULL;
+     Isolate::Current()->set_debugger_agent_instance(NULL);
      delete server_;
   }
 
@@ -77,8 +77,6 @@
   Semaphore* terminate_now_;  // Semaphore to signal termination.
   Semaphore* listening_;
 
-  static DebuggerAgent* instance_;
-
   friend class DebuggerAgentSession;
   friend void DebuggerAgentMessageHandler(const v8::Debug::Message& message);
 
@@ -90,8 +88,8 @@
 // debugger and sends debugger events/responses to the remote debugger.
 class DebuggerAgentSession: public Thread {
  public:
-  DebuggerAgentSession(DebuggerAgent* agent, Socket* client)
-      : Thread("v8:DbgAgntSessn"),
+  DebuggerAgentSession(Isolate* isolate, DebuggerAgent* agent, Socket* client)
+      : Thread(isolate, "v8:DbgAgntSessn"),
         agent_(agent), client_(client) {}
 
   void DebuggerMessage(Vector<uint16_t> message);
@@ -112,8 +110,8 @@
 // Utility methods factored out to be used by the D8 shell as well.
 class DebuggerAgentUtil {
  public:
-  static const char* kContentLength;
-  static int kContentLengthSize;
+  static const char* const kContentLength;
+  static const int kContentLengthSize;
 
   static SmartPointer<char> ReceiveMessage(const Socket* conn);
   static bool SendConnectMessage(const Socket* conn,