Adds CaptureClientObserver as a way to track changes in capture

ui/wm/core/capture_controller.h

 // Copyright (c) 2012 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_WM_CORE_CAPTURE_CONTROLLER_H_
 #define UI_WM_CORE_CAPTURE_CONTROLLER_H_
 
 #include <map>
 
-#include "base/compiler_specific.h"
 #include "base/macros.h"
+#include "base/observer_list.h"
 #include "ui/aura/client/capture_client.h"
 #include "ui/aura/window_observer.h"
 #include "ui/wm/wm_export.h"
 
 namespace aura {
 namespace client {
 class CaptureDelegate;
 }
 }
 
@@ skipping 10 matching lines @@
 
   // Returns true if this CaptureController is installed on at least one
   // root window.
   bool is_active() const { return !delegates_.empty(); }
 
   // Overridden from aura::client::CaptureClient:
   void SetCapture(aura::Window* window) override;
   void ReleaseCapture(aura::Window* window) override;
   aura::Window* GetCaptureWindow() override;
   aura::Window* GetGlobalCaptureWindow() override;
+  void AddObserver(aura::client::CaptureClientObserver* observer) override;
+  void RemoveObserver(aura::client::CaptureClientObserver* observer) override;
 
  private:
   friend class ScopedCaptureClient;
 
   CaptureController();
   ~CaptureController() override;
 
   // The current capture window. NULL if there is no capture window.
   aura::Window* capture_window_;
 
   // The capture delegate for the root window with native capture. The root
   // window with native capture may not contain |capture_window_|. This occurs
   // if |capture_window_| is reparented to a different root window while it has
   // capture.
   aura::client::CaptureDelegate* capture_delegate_;
 
   // The delegates notified when capture changes.
   std::map<aura::Window*, aura::client::CaptureDelegate*> delegates_;
 
+  base::ObserverList<aura::client::CaptureClientObserver> observers_;
+
   DISALLOW_COPY_AND_ASSIGN(CaptureController);
 };
 
 // ScopedCaptureClient is responsible for creating a CaptureClient for a
 // RootWindow. Specifically it creates a single CaptureController that is shared
 // among all ScopedCaptureClients and adds the RootWindow to it.
 class WM_EXPORT ScopedCaptureClient : public aura::WindowObserver {
  public:
   class WM_EXPORT TestApi {
    public:
@@ skipping 32 matching lines @@
 
   // RootWindow this ScopedCaptureClient was create for.
   aura::Window* root_window_;
 
   DISALLOW_COPY_AND_ASSIGN(ScopedCaptureClient);
 };
 
 }  // namespace wm
 
 #endif  // UI_WM_CORE_CAPTURE_CONTROLLER_H_