Do not activate system tray bubble by default

ash/common/system/tray/system_tray.h

Index: ash/common/system/tray/system_tray.h
diff --git a/ash/common/system/tray/system_tray.h b/ash/common/system/tray/system_tray.h
index 6d08cebec4d38cdbad35fa905e98a9b83593320d..c6730bdcbd4ee2dd1863657060436869dfcdea4f 100644
--- a/ash/common/system/tray/system_tray.h
+++ b/ash/common/system/tray/system_tray.h
@@ -19,6 +19,7 @@
 
 namespace ash {
 
+class KeyEventWatcher;
 enum class LoginStatus;
 class ScreenTrayItem;
 class SystemBubbleWrapper;
@@ -167,7 +168,15 @@ class ASH_EXPORT SystemTray : public TrayBackgroundView,
   TrayDate* GetTrayDateForTesting() const;
   TrayUpdate* GetTrayUpdateForTesting() const;
 
+  // Activate the system tay bubble.

[James Cook, 2016/09/22 21:17:16]

nit: tay -> tray

[oshima, 2016/09/23 09:37:20]

Done.

+  void ActivateBubble();
+
  private:
+  void CloseBubble(const ui::KeyEvent& key_event);

[James Cook, 2016/09/22 21:17:16]

nit: document. For example, why is it different than CloseSystemBubble.

[oshima, 2016/09/23 09:37:20]

Done.

+
+  // Acitavates the bubble and starts key navigation with the |key_event|.

[James Cook, 2016/09/22 21:17:16]

nit: activates

[oshima, 2016/09/23 09:37:20]

Done.

+  void ActivateAndStartNavigation(const ui::KeyEvent& key_event);
+
   // Creates the default set of items for the sytem tray.
   void CreateItems(SystemTrayDelegate* delegate);
 
@@ -263,6 +272,8 @@ class ASH_EXPORT SystemTray : public TrayBackgroundView,
   ScreenTrayItem* screen_capture_tray_item_;  // not owned
   ScreenTrayItem* screen_share_tray_item_;    // not owned
 
+  std::unique_ptr<KeyEventWatcher> key_event_watcher_;
+
   DISALLOW_COPY_AND_ASSIGN(SystemTray);
 };