Implement callback when script finishes running in V8 API.

src/v8.h

Index: src/v8.h
diff --git a/src/v8.h b/src/v8.h
index 71e7fe4bf4ba99c54dd3eeca4245e1cb5c1875cb..582e97319c2256019dd66882ff988160f249f4e2 100644
--- a/src/v8.h
+++ b/src/v8.h
@@ -108,6 +108,10 @@ class V8 : public AllStatic {
   // Idle notification directly from the API.
   static bool IdleNotification(int hint);
 
+  static void AddCallCompletedCallback(CallCompletedCallback callback);
+  static void RemoveCallCompletedCallback(CallCompletedCallback callback);
+  static void FireCallCompletedCallback(Isolate* isolate);
+
  private:
   static void InitializeOncePerProcess();
 
@@ -123,6 +127,8 @@ class V8 : public AllStatic {
   static bool has_been_disposed_;
   // True if we are using the crankshaft optimizing compiler.
   static bool use_crankshaft_;
+  // List of callbacks when a call completes.
+  static List<CallCompletedCallback>* call_completed_callbacks_;
 };