Make DispatchKeyEventPostIME() asynchronous.

ui/base/ime/input_method_delegate.h

 // Copyright (c) 2011 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 UI_BASE_IME_INPUT_METHOD_DELEGATE_H_
 #define UI_BASE_IME_INPUT_METHOD_DELEGATE_H_
 
 #include "ui/base/ime/ui_base_ime_export.h"
 #include "ui/events/event_dispatcher.h"
 
 namespace ui {
 
 class KeyEvent;
 
 namespace internal {
 
 // An interface implemented by the object that handles events sent back from an
 // ui::InputMethod implementation.
 class UI_BASE_IME_EXPORT InputMethodDelegate {
  public:
   virtual ~InputMethodDelegate() {}
 
   // Dispatch a key event already processed by the input method.
   // Returns true if the event was processed.
   virtual ui::EventDispatchDetails DispatchKeyEventPostIME(
       ui::KeyEvent* key_event) = 0;
+
+  virtual ui::EventDispatchDetails DispatchKeyEventPostIME(

[Shu Chen, 2017/07/06 03:38:42]

Anything makes you decide not to keep InputMethodDelegate as an interface?

+      ui::KeyEvent* key_event,
+      std::unique_ptr<base::Callback<void(bool)>> ack_callback);
 };
 
 }  // namespace internal
 }  // namespace ui
 
 #endif  // UI_BASE_IME_INPUT_METHOD_DELEGATE_H_