Update V8 to r3121 as required for WebKit update.

Change-Id: Ic53e0aef9a9eb9b71ee7d25a8aef61520bba899c
diff --git a/src/assembler.h b/src/assembler.h
index 827389a..21a66dd 100644
--- a/src/assembler.h
+++ b/src/assembler.h
@@ -191,6 +191,7 @@
   INLINE(Address target_address());
   INLINE(void set_target_address(Address target));
   INLINE(Object* target_object());
+  INLINE(Handle<Object> target_object_handle(Assembler* origin));
   INLINE(Object** target_object_address());
   INLINE(void set_target_object(Object* target));
 
@@ -216,10 +217,10 @@
 
   // Patch the code with a call.
   void PatchCodeWithCall(Address target, int guard_bytes);
-  // Check whether the current instruction is currently a call
-  // sequence (whether naturally or a return sequence overwritten
-  // to enter the debugger).
-  INLINE(bool IsCallInstruction());
+
+  // Check whether this return sequence has been patched
+  // with a call to the debugger.
+  INLINE(bool IsPatchedReturnSequence());
 
 #ifdef ENABLE_DISASSEMBLER
   // Printing