Adds CaptureClientObserver as a way to track changes in capture

ui/views/widget/desktop_aura/desktop_capture_client.cc

 // Copyright 2013 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/views/widget/desktop_aura/desktop_capture_client.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"
@@ skipping 80 matching lines @@
 
 aura::Window* DesktopCaptureClient::GetGlobalCaptureWindow() {
   for (CaptureClients::iterator i = capture_clients_->begin();
        i != capture_clients_->end(); ++i) {
     if ((*i)->capture_window_)
       return (*i)->capture_window_;
   }
   return NULL;
 }
 
+void DesktopCaptureClient::AddObserver(
+    aura::client::CaptureClientObserver* observer) {
+  NOTREACHED();
+}
+
+void DesktopCaptureClient::RemoveObserver(
+    aura::client::CaptureClientObserver* observer) {
+  NOTREACHED();
+}
+
 }  // namespace views