[mojo-bindings] Use Watcher API for JS bindings

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/macros.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/message_pump/handle_watcher.h"
 #include "mojo/public/cpp/system/core.h"
+#include "mojo/public/cpp/system/watcher.h"
 
 namespace mojo {
 namespace edk {
 namespace js {
 
 class WaitingCallback : public gin::Wrappable<WaitingCallback>,
                         public HandleCloseObserver {
  public:
   static gin::WrapperInfo kWrapperInfo;
 
   // Creates a new WaitingCallback.
+  //
+  // If |one_shot| is true, the callback will only ever be called at most once.
+  // If false, the callback may be called any number of times until the
+  // WaitingCallback is explicitly cancelled.
   static gin::Handle<WaitingCallback> Create(
       v8::Isolate* isolate,
       v8::Handle<v8::Function> callback,
       gin::Handle<HandleWrapper> handle_wrapper,
-      MojoHandleSignals signals);
+      MojoHandleSignals signals,
+      bool one_shot);
 
   // Cancels the callback. Does nothing if a callback is not pending. This is
   // implicitly invoked from the destructor but can be explicitly invoked as
   // necessary.
   void Cancel();
 
  private:
   WaitingCallback(v8::Isolate* isolate,
                   v8::Handle<v8::Function> callback,
-                  gin::Handle<HandleWrapper> handle_wrapper);
+                  gin::Handle<HandleWrapper> handle_wrapper,
+                  bool one_shot);
   ~WaitingCallback() override;
 
   // Callback from common::HandleWatcher.
   void OnHandleReady(MojoResult result);
 
   // Invoked by the HandleWrapper if the handle is closed while this wait is
   // still in progress.
   void OnWillCloseHandle() override;
 
   void RemoveHandleCloseObserver();
   void CallCallback(MojoResult result);
 
+  // Indicates whether this is a one-shot callback or not. If so, it uses the

[yzshen1, 2016/03/08 22:37:25]

It seems straightforward to use the new Watcher API to also support one-shot
watch. Is there reason not the directly remove the common::HandleWatcher code?

(But I am okay with this if you believe the current way is easier to move
forward.)

+  // deprecated HandleWatcher to wait for signals; otherwise it uses the new
+  // system Watcher API.
+  const bool one_shot_;
+
   base::WeakPtr<gin::Runner> runner_;
 
   common::HandleWatcher handle_watcher_;
+  Watcher watcher_;
 
   HandleWrapper* handle_wrapper_;
   base::WeakPtrFactory<WaitingCallback> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(WaitingCallback);
 };
 
 }  // namespace js
 }  // namespace edk
 }  // namespace mojo
 
 #endif  // MOJO_EDK_JS_WAITING_CALLBACK_H_