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

chrome/browser/ui/input_method/input_method_engine_base.cc

 // Copyright 2016 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/ui/input_method/input_method_engine_base.h"
 
 #include <memory>
 
 #undef FocusIn
 #undef FocusOut
@@ skipping 424 matching lines @@
   if (!IsActive() ||
       (context_id != 0 && (context_id != context_id_ || context_id_ == -1)))
     return false;
 
   for (size_t i = 0; i < events.size(); ++i) {
     const KeyboardEvent& event = events[i];
     const ui::EventType type =
         (event.type == "keyup") ? ui::ET_KEY_RELEASED : ui::ET_KEY_PRESSED;
     ui::KeyboardCode key_code = static_cast<ui::KeyboardCode>(event.key_code);
 
-    int flags = ui::EF_NONE;
+    int flags = ui::EF_IS_SYNTHESIZED;
     flags |= event.alt_key ? ui::EF_ALT_DOWN : ui::EF_NONE;
     flags |= event.ctrl_key ? ui::EF_CONTROL_DOWN : ui::EF_NONE;
     flags |= event.shift_key ? ui::EF_SHIFT_DOWN : ui::EF_NONE;
     flags |= event.caps_lock ? ui::EF_CAPS_LOCK_ON : ui::EF_NONE;
 
     ui::KeyEvent ui_event(
         type, key_code, ui::KeycodeConverter::CodeStringToDomCode(event.code),
         flags, ui::KeycodeConverter::KeyStringToDomKey(event.key),
         ui::EventTimeForNow());
     base::AutoReset<const ui::KeyEvent*> reset_sent_key(&sent_key_event_,
                                                         &ui_event);
     if (!SendKeyEvent(&ui_event, event.code))
       return false;
   }
   return true;
 }
 
 }  // namespace input_method