Adds CaptureClientObserver as a way to track changes in capture

ui/wm/core/capture_controller.cc

 // 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.
 
 #include "ui/wm/core/capture_controller.h"
 
+#include "ui/aura/client/capture_client_observer.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_event_dispatcher.h"
 #include "ui/aura/window_tracker.h"
 #include "ui/aura/window_tree_host.h"
 
 namespace wm {
 
 ////////////////////////////////////////////////////////////////////////////////
 // CaptureController, public:
 
@@ skipping 48 matching lines @@
 
   for (const auto& it : delegates)
     it.second->UpdateCapture(old_capture_window, new_capture_window);
 
   if (capture_delegate_ != old_capture_delegate) {
     if (old_capture_delegate)
       old_capture_delegate->ReleaseNativeCapture();
     if (capture_delegate_)
       capture_delegate_->SetNativeCapture();
   }
+
+  for (aura::client::CaptureClientObserver& observer : observers_)
+    observer.OnCaptureChanged(old_capture_window, capture_window_);
 }
 
 void CaptureController::ReleaseCapture(aura::Window* window) {
   if (capture_window_ != window)
     return;
   SetCapture(nullptr);
 }
 
 aura::Window* CaptureController::GetCaptureWindow() {
   return capture_window_;
 }
 
 aura::Window* CaptureController::GetGlobalCaptureWindow() {
   return capture_window_;
 }
 
+void CaptureController::AddObserver(
+    aura::client::CaptureClientObserver* observer) {
+  observers_.AddObserver(observer);
+}
+
+void CaptureController::RemoveObserver(
+    aura::client::CaptureClientObserver* observer) {
+  observers_.RemoveObserver(observer);
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // CaptureController, private:
 
 CaptureController::CaptureController()
     : capture_window_(nullptr),
       capture_delegate_(nullptr) {
 }
 
 CaptureController::~CaptureController() {
 }
@@ skipping 41 matching lines @@
 
 ///////////////////////////////////////////////////////////////////////////////
 // CaptureController::TestApi
 
 void ScopedCaptureClient::TestApi::SetDelegate(
     aura::client::CaptureDelegate* delegate) {
   client_->capture_controller_->delegates_[client_->root_window_] = delegate;
 }
 
 }  // namespace wm