Replace Ash web notification tray view with a button.

ash/system/web_notification/web_notification_tray.h

Index: ash/system/web_notification/web_notification_tray.h
diff --git a/ash/system/web_notification/web_notification_tray.h b/ash/system/web_notification/web_notification_tray.h
index 1cfdab14f90b770adb8dd62d5bbbc58dad366c1b..b76a7143a14d110781b72d61c0d0face61e43bb5 100644
--- a/ash/system/web_notification/web_notification_tray.h
+++ b/ash/system/web_notification/web_notification_tray.h
@@ -20,7 +20,7 @@ class ImageSkia;
 }
 
 namespace views {
-class Label;
+class ImageButton;
 }
 
 namespace ash {
@@ -43,7 +43,8 @@ class WebNotificationView;
 // generated by SystemTrayItem). Visibility of one notification type or other
 // is controlled by StatusAreaWidget.
 
-class ASH_EXPORT WebNotificationTray : public internal::TrayBackgroundView {
+class ASH_EXPORT WebNotificationTray : public internal::TrayBackgroundView,
+                                       public views::ButtonListener {
  public:
   class Delegate {
    public:
@@ -121,6 +122,10 @@ class ASH_EXPORT WebNotificationTray : public internal::TrayBackgroundView {
   // Overridden from internal::ActionableView.
   virtual bool PerformAction(const ui::Event& event) OVERRIDE;
 
+  // Overridden from ButtonListener.
+  virtual void ButtonPressed(views::Button* sender,
+                             const ui::Event& event) OVERRIDE;
+
   // Constants exposed for unit tests:
   static const size_t kMaxVisibleTrayNotifications;
   static const size_t kMaxVisiblePopupNotifications;
@@ -155,6 +160,9 @@ class ASH_EXPORT WebNotificationTray : public internal::TrayBackgroundView {
   // Called when a notification is clicked on. Event is passed to the Delegate.
   void OnClicked(const std::string& id);
 
+  // Shows or hides the message center bubble.
+  void ToggleMessageCenterBubble();
+
   // Shows or updates the message center bubble and hides the popup bubble.
   void ShowMessageCenterBubble();
 
@@ -194,7 +202,7 @@ class ASH_EXPORT WebNotificationTray : public internal::TrayBackgroundView {
   scoped_ptr<internal::WebNotificationList> notification_list_;
   scoped_ptr<MessageCenterBubble> message_center_bubble_;
   scoped_ptr<PopupBubble> popup_bubble_;
-  views::Label* count_label_;
+  views::ImageButton* button_;
   Delegate* delegate_;
   bool show_message_center_on_unlock_;