Do not activate system tray bubble by default

ash/mus/bridge/wm_shell_mus.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 "ash/mus/bridge/wm_shell_mus.h"
 
 #include <utility>
 
 #include "ash/common/accelerators/accelerator_controller.h"
+#include "ash/common/key_event_watcher.h"
 #include "ash/common/session/session_state_delegate.h"
 #include "ash/common/shell_delegate.h"
 #include "ash/common/shell_observer.h"
 #include "ash/common/shell_window_ids.h"
 #include "ash/common/system/tray/system_tray_delegate.h"
 #include "ash/common/wallpaper/wallpaper_delegate.h"
 #include "ash/common/wm/maximize_mode/maximize_mode_event_handler.h"
 #include "ash/common/wm/maximize_mode/scoped_disable_internal_mouse_and_keyboard.h"
 #include "ash/common/wm/mru_window_tracker.h"
 #include "ash/common/wm/window_cycle_event_filter.h"
@@ skipping 337 matching lines @@
     WmWindow* workspace_window) {
   return base::MakeUnique<WorkspaceEventHandlerMus>(
       WmWindowMus::GetMusWindow(workspace_window));
 }
 
 std::unique_ptr<ImmersiveFullscreenController>
 WmShellMus::CreateImmersiveFullscreenController() {
   return base::MakeUnique<ImmersiveFullscreenController>();
 }
 
+std::unique_ptr<KeyEventWatcher> WmShellMus::CreateKeyEventWatcher() {
+  // TODO: needs implementation for mus, http://crbug.com/649600.
+  NOTIMPLEMENTED();
+  return std::unique_ptr<KeyEventWatcher>();
+}
+
 void WmShellMus::OnOverviewModeStarting() {
   FOR_EACH_OBSERVER(ShellObserver, *shell_observers(),
                     OnOverviewModeStarting());
 }
 
 void WmShellMus::OnOverviewModeEnded() {
   FOR_EACH_OBSERVER(ShellObserver, *shell_observers(), OnOverviewModeEnded());
 }
 
 SessionStateDelegate* WmShellMus::GetSessionStateDelegate() {
@@ skipping 69 matching lines @@
                     OnWindowActivated(gained_active, lost_active));
 }
 
 void WmShellMus::OnDidDestroyClient(ui::WindowTreeClient* client) {
   DCHECK_EQ(window_tree_client(), client);
   client->RemoveObserver(this);
 }
 
 }  // namespace mus
 }  // namespace ash