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

chrome/browser/extensions/api/virtual_keyboard_private/chrome_virtual_keyboard_delegate.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 "chrome/browser/extensions/api/virtual_keyboard_private/chrome_virtual_keyboard_delegate.h"
 
 #include <string>
 #include <utility>
 
 #include "ash/shell.h"
@@ skipping 137 matching lines @@
                                                  int char_value,
                                                  int key_code,
                                                  const std::string& key_name,
                                                  int modifiers) {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   aura::Window* window = GetKeyboardContainer();
   return window && keyboard::SendKeyEvent(type,
                                           char_value,
                                           key_code,
                                           key_name,
-                                          modifiers,
+                                          modifiers & ui::EF_IS_SYNTHESIZED,

[Shu Chen, 2016/08/23 02:56:58]

You need to do the same thing in here: 
https://cs.chromium.org/chromium/src/chrome/browser/chromeos/input_method/inp....

[Evan Stade, 2016/08/23 03:38:21]

thanks, done in InputMethodEngineBase::SendKeyEvents. I don't know how to verify
this is correct though.

                                           window->GetHost());
 }
 
 bool ChromeVirtualKeyboardDelegate::ShowLanguageSettings() {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
   content::RecordAction(base::UserMetricsAction("OpenLanguageOptionsDialog"));
   chrome::ShowSettingsSubPageForProfile(ProfileManager::GetActiveUserProfile(),
                                         chrome::kLanguageOptionsSubPage);
   return true;
 }
@@ skipping 27 matching lines @@
 }
 
 bool ChromeVirtualKeyboardDelegate::IsLanguageSettingsEnabled() {
   return (user_manager::UserManager::Get()->IsUserLoggedIn() &&
           !chromeos::UserAddingScreen::Get()->IsRunning() &&
           !(chromeos::ScreenLocker::default_screen_locker() &&
             chromeos::ScreenLocker::default_screen_locker()->locked()));
 }
 
 }  // namespace extensions