Fix uber tray to accept focus via tab selection

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 58049ec3f0150eac8ec62838ac629099a497b901..0c0158adb4042cf2d675b2125515167933928f41 100644
--- a/ash/system/tray/system_tray.h
+++ b/ash/system/tray/system_tray.h
@@ -79,8 +79,12 @@ class ASH_EXPORT SystemTray : NON_EXPORTED_BASE(
       bool value,
       internal::BackgroundAnimator::ChangeType change_type);
 
+  // Take focus and activate the system tray.
+  void TakeFocus(View* next_focusable_view);
+
   // Returns true if the launcher should show.
   bool should_show_launcher() const { return popup_ && should_show_launcher_; }
+  bool is_taking_focus() const { return taking_focus_; }
 
   AccessibilityObserver* accessibility_observer() const {
     return accessibility_observer_;
@@ -174,6 +178,9 @@ class ASH_EXPORT SystemTray : NON_EXPORTED_BASE(
   // See description agove getter.
   bool should_show_launcher_;
 
+  // Set when taking focus to indicate that the system area can be activated.
+  bool taking_focus_;
+
   internal::BackgroundAnimator hide_background_animator_;
   internal::BackgroundAnimator hover_background_animator_;