Revert of Remove InputMethodEventHandler.

ui/aura/window_tree_host.h

 // Copyright (c) 2012 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_AURA_WINDOW_TREE_HOST_H_
 #define UI_AURA_WINDOW_TREE_HOST_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 139 matching lines @@
   // can make sure the correct InputMethod instance processes the key event no
   // matter which WindowTreeHost is the target for event. Please refer to the
   // test: ExtendedDesktopTest.KeyEventsOnLockScreen.
   //
   // TODO(shuchen): remove this method after above reasons become invalid.
   // A possible solution is to make sure DrmWindowHost can find the correct
   // WindowTreeHost to dispatch events.
   void SetSharedInputMethod(ui::InputMethod* input_method);
 
   // Overridden from ui::internal::InputMethodDelegate:
-  ui::EventDispatchDetails DispatchKeyEventPostIME(ui::KeyEvent* event) final;
+  ui::EventDispatchDetails DispatchKeyEventPostIME(
+      ui::KeyEvent* event) override;
 
   // Returns the EventSource responsible for dispatching events to the window
   // tree.
   virtual ui::EventSource* GetEventSource() = 0;
 
   // Returns the accelerated widget.
   virtual gfx::AcceleratedWidget GetAcceleratedWidget() = 0;
 
   // Shows the WindowTreeHost.
   void Show();
@@ skipping 94 matching lines @@
   bool owned_input_method_;
 
   gfx::Insets output_surface_padding_in_pixels_;
 
   DISALLOW_COPY_AND_ASSIGN(WindowTreeHost);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_WINDOW_TREE_HOST_H_