Mojo: Cancel WaitingCallbacks when their HandleWrappers are closed.

mojo/bindings/js/handle.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_BINDINGS_JS_HANDLE_H_
 #define MOJO_BINDINGS_JS_HANDLE_H_
 
+#include "base/observer_list.h"
 #include "gin/converter.h"
 #include "gin/handle.h"
 #include "gin/wrappable.h"
 #include "mojo/public/cpp/system/core.h"
 
 namespace gin {
+class HandleCloseObserver;
 
 // Wrapper for mojo Handles exposed to JavaScript. This ensures the Handle
 // is Closed when its JS object is garbage collected.
 class HandleWrapper : public gin::Wrappable<HandleWrapper> {
  public:
   static gin::WrapperInfo kWrapperInfo;
 
   static gin::Handle<HandleWrapper> Create(v8::Isolate* isolate,
                                            MojoHandle handle) {
     return gin::CreateHandle(isolate, new HandleWrapper(handle));
   }
 
   mojo::Handle get() const { return handle_.get(); }
   mojo::Handle release() { return handle_.release(); }
-  void Close() { handle_.reset(); }
+  void Close();
+
+  void AddCloseObserver(HandleCloseObserver* observer);
+  void RemoveCloseObserver(HandleCloseObserver* observer);
 
  protected:
   HandleWrapper(MojoHandle handle);
   virtual ~HandleWrapper();
+  void NotifyCloseObservers();
+
   mojo::ScopedHandle handle_;
+  ObserverList<HandleCloseObserver> close_observers_;
 };
 
 // Note: It's important to use this converter rather than the one for
 // MojoHandle, since that will do a simple int32 conversion. It's unfortunate
 // there's no way to prevent against accidental use.
 // TODO(mpcomplete): define converters for all Handle subtypes.
 template<>
 struct Converter<mojo::Handle> {
   static v8::Handle<v8::Value> ToV8(v8::Isolate* isolate,
                                     const mojo::Handle& val);
@@ skipping 22 matching lines @@
       return false;
     }
     *out = gin::Handle<gin::HandleWrapper>(val, object);
     return true;
   }
 };
 
 }  // namespace gin
 
 #endif  // MOJO_BINDINGS_JS_HANDLE_H_