Refuse to show Alt+Tab UI concurrently with virtual keyboard.

ui/keyboard/keyboard_util.cc

 // Copyright (c) 2013 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 "ui/keyboard/keyboard_util.h"
 
 #include <string>
 
 #include "base/command_line.h"
 #include "base/lazy_instance.h"
@@ skipping 15 matching lines @@
 #include "ui/keyboard/keyboard_switches.h"
 #include "ui/keyboard/keyboard_ui.h"
 
 namespace {
 
 const char kKeyDown[] ="keydown";
 const char kKeyUp[] = "keyup";
 
 void SendProcessKeyEvent(ui::EventType type,
                          aura::WindowTreeHost* host) {
+NOTIMPLEMENTED() << " SENDING";

[oshima, 2016/08/23 04:53:43]

nit: debug log?

   ui::KeyEvent event(type, ui::VKEY_PROCESSKEY, ui::DomCode::NONE,
                      ui::EF_IS_SYNTHESIZED, ui::DomKey::PROCESS,
                      ui::EventTimeForNow());
   ui::EventDispatchDetails details =
       host->event_processor()->OnEventFromSource(&event);
   CHECK(!details.dispatcher_destroyed);
 }
 
 base::LazyInstance<base::Time> g_keyboard_load_time_start =
     LAZY_INSTANCE_INITIALIZER;
@@ skipping 326 matching lines @@
 }
 
 void LogKeyboardControlEvent(KeyboardControlEvent event) {
   UMA_HISTOGRAM_ENUMERATION(
       "VirtualKeyboard.KeyboardControlEvent",
       event,
       keyboard::KEYBOARD_CONTROL_MAX);
 }
 
 }  // namespace keyboard