Implements a new API to set a function entry hook for profiling.

src/code-stubs.h

Index: src/code-stubs.h
diff --git a/src/code-stubs.h b/src/code-stubs.h
index 5a076d2f1387fba5b3d16f7b9935867aab99a5f9..f19063230a7d953d7dabe5c152c6e0eaf8798bc9 100644
--- a/src/code-stubs.h
+++ b/src/code-stubs.h
@@ -73,7 +73,8 @@ namespace internal {
   V(DebuggerStatement)                   \
   V(StringDictionaryLookup)              \
   V(ElementsTransitionAndStore)          \
-  V(StoreArrayLiteralElement)
+  V(StoreArrayLiteralElement)            \
+  V(ProfileEntryHook)
 
 // List of code stubs only used on ARM platforms.
 #ifdef V8_TARGET_ARCH_ARM
@@ -1142,6 +1143,37 @@ class StoreArrayLiteralElementStub : public CodeStub {
   DISALLOW_COPY_AND_ASSIGN(StoreArrayLiteralElementStub);
 };
 
+
+class ProfileEntryHookStub : public CodeStub {
+ public:
+  explicit ProfileEntryHookStub() {}
+
+  // The profile entry hook function is not allowed to cause a GC.
+  virtual bool SometimesSetsUpAFrame() { return false; }
+
+  // Generates a call to the entry hook if it's enabled.
+  static void MaybeCallEntryHook(MacroAssembler* masm);
+
+  // Sets or unsets the entry hook function. Returns true on success,
+  // false on an attempt to replace a non-NULL entry hook with another
+  // non-NULL hook.
+  static bool SetFunctionEntryHook(FunctionEntryHook entry_hook);
+
+ private:
+  static void EntryHookTrampoline(intptr_t function,
+                                  intptr_t stack_pointer);
+
+  Major MajorKey() { return ProfileEntryHook; }
+  int MinorKey() { return 0; }
+
+  void Generate(MacroAssembler* masm);
+
+  // The current function entry hook.
+  static FunctionEntryHook entry_hook_;
+
+  DISALLOW_COPY_AND_ASSIGN(ProfileEntryHookStub);
+};
+
 } }  // namespace v8::internal
 
 #endif  // V8_CODE_STUBS_H_