Fix WaitingCallback to not run JavaScript during GC

mojo/edk/js/waiting_callback.h

 // Copyright 2014 The Chromium 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 MOJO_EDK_JS_WAITING_CALLBACK_H_
 #define MOJO_EDK_JS_WAITING_CALLBACK_H_
 
+#include "base/memory/weak_ptr.h"
 #include "gin/handle.h"
 #include "gin/runner.h"
 #include "gin/wrappable.h"
 #include "mojo/edk/js/handle.h"
 #include "mojo/edk/js/handle_close_observer.h"
 #include "mojo/public/c/environment/async_waiter.h"
 #include "mojo/public/cpp/system/core.h"
 
 namespace mojo {
 namespace js {
@@ skipping 24 matching lines @@
   // Callback from MojoAsyncWaiter. |closure| is the WaitingCallback.
   static void CallOnHandleReady(void* closure, MojoResult result);
 
   // Invoked from CallOnHandleReady() (CallOnHandleReady() must be static).
   void OnHandleReady(MojoResult result);
 
   // Invoked by the HandleWrapper if the handle is closed while this wait is
   // still in progress.
   void OnWillCloseHandle() override;
 
+  void ClearWaitId();
+  void CallCallback(MojoResult result);
+
   base::WeakPtr<gin::Runner> runner_;
   MojoAsyncWaitID wait_id_;
 
   HandleWrapper* handle_wrapper_;
+  base::WeakPtrFactory<WaitingCallback> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(WaitingCallback);
 };
 
 }  // namespace js
 }  // namespace mojo
 
 #endif  // MOJO_EDK_JS_WAITING_CALLBACK_H_