Implement TOGGLE_EXPANSION action for the ARC notifications.

ui/arc/notification/arc_custom_notification_view.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_ARC_NOTIFICATION_ARC_CUSTOM_NOTIFICATION_VIEW_H_
 #define UI_ARC_NOTIFICATION_ARC_CUSTOM_NOTIFICATION_VIEW_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 67 matching lines @@
       const ViewHierarchyChangedDetails& details) override;
   void Layout() override;
   void OnPaint(gfx::Canvas* canvas) override;
   void OnKeyEvent(ui::KeyEvent* event) override;
   void OnGestureEvent(ui::GestureEvent* event) override;
   void OnMouseEntered(const ui::MouseEvent& event) override;
   void OnMouseExited(const ui::MouseEvent& event) override;
   void OnFocus() override;
   void OnBlur() override;
   views::FocusTraversable* GetFocusTraversable() override;
+  bool OnMousePressed(const ui::MouseEvent& event) override;
 
   // views::ButtonListener
   void ButtonPressed(views::Button* sender, const ui::Event& event) override;
 
   // aura::WindowObserver
   void OnWindowBoundsChanged(aura::Window* window,
                              const gfx::Rect& old_bounds,
                              const gfx::Rect& new_bounds) override;
   void OnWindowDestroying(aura::Window* window) override;
 
@@ skipping 33 matching lines @@
 
   // Protects from call loops between Layout and OnWindowBoundsChanged.
   bool in_layout_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(ArcCustomNotificationView);
 };
 
 }  // namespace arc
 
 #endif  // UI_ARC_NOTIFICATION_ARC_CUSTOM_NOTIFICATION_VIEW_H_