Use EventHandler for IME

ash/host/ash_window_tree_host.cc

 // 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.
 
 #include "ash/host/ash_window_tree_host.h"
 
 #include "ui/aura/client/screen_position_client.h"
 #include "ui/aura/window_tree_host.h"
 #include "ui/events/event.h"
 #include "ui/gfx/geometry/rect.h"
 
 namespace ash {
 
+AshWindowTreeHost::AshWindowTreeHost() : input_method_handler_(nullptr) {
+}
+
 void AshWindowTreeHost::TranslateLocatedEvent(ui::LocatedEvent* event) {
   if (event->IsTouchEvent())
     return;
 
   aura::WindowTreeHost* wth = AsWindowTreeHost();
   aura::Window* root_window = wth->window();
   aura::client::ScreenPositionClient* screen_position_client =
       aura::client::GetScreenPositionClient(root_window);
   gfx::Rect local(wth->GetBounds().size());
   local.Inset(GetHostInsets());
 
   if (screen_position_client && !local.Contains(event->location())) {
     gfx::Point location(event->location());
     // In order to get the correct point in screen coordinates
     // during passive grab, we first need to find on which host window
     // the mouse is on, and find out the screen coordinates on that
     // host window, then convert it back to this host window's coordinate.
     screen_position_client->ConvertHostPointToScreen(root_window, &location);
     screen_position_client->ConvertPointFromScreen(root_window, &location);
     wth->ConvertPointToHost(&location);
     event->set_location(location);
     event->set_root_location(location);
   }
 }
 
 }  // namespace ash