[promisehook] Implement PromiseHook

src/promise-utils.h

 // Copyright 2016 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.
 
 #ifndef V8_PROMISE_UTILS_H_
 #define V8_PROMISE_UTILS_H_
 
 #include "src/contexts.h"
 #include "src/objects.h"
 
@@ skipping 11 matching lines @@
     kPromiseSlot,
 
     // Whether to trigger a debug event or not. Used in catch
     // prediction.
     kDebugEventSlot,
     kPromiseContextLength,
   };
 
   // These get and set the slots on the PromiseResolvingContext, which
   // is used by the resolve/reject promise callbacks.
-  static JSObject* GetPromise(Handle<Context> context);
+  static JSPromise* GetPromise(Handle<Context> context);
   static Object* GetDebugEvent(Handle<Context> context);
   static bool HasAlreadyVisited(Handle<Context> context);
   static void SetAlreadyVisited(Handle<Context> context);
 
   static void CreateResolvingFunctions(Isolate* isolate,
                                        Handle<JSObject> promise,
                                        Handle<Object> debug_event,
                                        Handle<JSFunction>* resolve,
                                        Handle<JSFunction>* reject);
 };
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_PROMISE_UTILS_H_