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..d2a05a15d7d9db6e8b7cb29d65b1f24cebc20fac 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 +168,21 @@ class ASH_EXPORT SystemTray : public TrayBackgroundView,
   TrayDate* GetTrayDateForTesting() const;
   TrayUpdate* GetTrayUpdateForTesting() const;
 
+  // Activates the system tray bubble.
+  void ActivateBubble();
+
  private:
+  class ActivationObserver;
+
+  // Closes the bubble. Used to bind as a KeyEventWatcher::KeyEventCallback.
+  void CloseBubble(const ui::KeyEvent& key_event);
+
+  // Activates the bubble and starts key navigation with the |key_event|.
+  void ActivateAndStartNavigation(const ui::KeyEvent& key_event);
+
+  // Creates the key event watcher.

[James Cook, 2016/09/23 16:32:28]

nit: "See ShowItems() for why key events are observed."

[oshima, 2016/09/23 19:19:54]

Done.

+  void CreateKeyEventWatcher();
+
   // Creates the default set of items for the sytem tray.
   void CreateItems(SystemTrayDelegate* delegate);
 
@@ -192,10 +207,14 @@ class ASH_EXPORT SystemTray : public TrayBackgroundView,
 
   // Constructs or re-constructs |system_bubble_| and populates it with |items|.
   // Specify |change_tray_status| to true if want to change the tray background
-  // status.
+  // status. The bubble will be opened in inactive state. If |can_activate| is
+  // true, the bubble will be activated by one of following means.
+  // * When alt/alt-tab acclerator is used to start navigation.
+  // * When the bubble is opened by accelerator.
+  // * When the tray item is set to be focused.

[James Cook, 2016/09/23 16:32:28]

Nice documentation.

   void ShowItems(const std::vector<SystemTrayItem*>& items,
                  bool details,
-                 bool activate,
+                 bool can_activate,
                  BubbleCreationType creation_type,
                  int x_offset,
                  bool persistent);
@@ -263,6 +282,10 @@ 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_;
+
+  std::unique_ptr<ActivationObserver> activation_observer_;
+
   DISALLOW_COPY_AND_ASSIGN(SystemTray);
 };