Do not activate TrayBubbleView by default

ash/system/tray/system_tray.h

Index: ash/system/tray/system_tray.h
diff --git a/ash/system/tray/system_tray.h b/ash/system/tray/system_tray.h
index fa16c53f74067aaee8e1eacaccff91add8d1d17d..8483db9220a9666d30524d588ae785b695d249d9 100644
--- a/ash/system/tray/system_tray.h
+++ b/ash/system/tray/system_tray.h
@@ -18,7 +18,6 @@
 
 namespace ash {
 
-class KeyEventWatcher;
 enum class LoginStatus;
 class ScreenTrayItem;
 class SystemBubbleWrapper;
@@ -133,7 +132,12 @@ class ASH_EXPORT SystemTray : public TrayBackgroundView,
   void BubbleViewDestroyed() override;
   void OnMouseEnteredView() override;
   void OnMouseExitedView() override;
+  void RegisterAccelerators(const std::vector<ui::Accelerator>& accelerators,
+                            views::TrayBubbleView* tray_bubble_view) override;
+  void UnregisterAllAccelerators(
+      views::TrayBubbleView* tray_bubble_view) override;
   base::string16 GetAccessibleNameForBubble() override;
+  bool ShouldEnableExtraKeyboardAccessibility() override;
   void HideBubble(const views::TrayBubbleView* bubble_view) override;
 
   ScreenTrayItem* GetScreenShareItem() { return screen_share_tray_item_; }
@@ -152,10 +156,6 @@ class ASH_EXPORT SystemTray : public TrayBackgroundView,
   // Activates the bubble and starts key navigation with the |key_event|.
   void ActivateAndStartNavigation(const ui::KeyEvent& key_event);
 
-  // Creates the key event watcher. See |ShowItems()| for why key events are
-  // observed.
-  void CreateKeyEventWatcher();
-
   // Creates the default set of items for the sytem tray.
   void CreateItems(SystemTrayDelegate* delegate);
 
@@ -232,8 +232,6 @@ class ASH_EXPORT SystemTray : public TrayBackgroundView,
   ScreenTrayItem* screen_capture_tray_item_ = nullptr;  // not owned
   ScreenTrayItem* screen_share_tray_item_ = nullptr;    // not owned
 
-  std::unique_ptr<KeyEventWatcher> key_event_watcher_;
-
   std::unique_ptr<ActivationObserver> activation_observer_;
 
   DISALLOW_COPY_AND_ASSIGN(SystemTray);