Handle UNPIN operation in ash.

ash/wm/screen_pinning_controller.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 ASH_WM_SCREEN_PINNING_CONTROLLER_H_
 #define ASH_WM_SCREEN_PINNING_CONTROLLER_H_
 
 #include <memory>
 #include <vector>
 
@@ skipping 13 matching lines @@
                           WindowTreeHostManager* window_tree_host_manager);
   ~ScreenPinningController() override;
 
   // Sets a pinned window. It is not allowed to call this when there already
   // is a pinned window.
   void SetPinnedWindow(WmWindow* pinned_window);
 
   // Returns true if in pinned mode, otherwise false.
   bool IsPinned() const;
 
+  // Returns the pinned window if in pinned mode, or nullptr.
+  WmWindow* pinned_window() const { return pinned_window_; }
+
   // Called when a new window is added to the container which has the pinned
   // window.
   void OnWindowAddedToPinnedContainer(WmWindow* new_window);
 
   // Called when a window will be removed from the container which has the
   // pinned window.
   void OnWillRemoveWindowFromPinnedContainer(WmWindow* window);
 
   // Called when a window stacking is changed in the container which has the
   // pinned window.
@@ skipping 61 matching lines @@
   std::unique_ptr<SystemModalContainerChildWindowObserver>
       system_modal_container_child_window_observer_;
   std::unique_ptr<DimWindowObserver> dim_window_observer_;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenPinningController);
 };
 
 }  // namespace ash
 
 #endif  // ASH_WM_SCREEN_PINNING_CONTROLLER_H_