Moves maintaining ShellObservers back to Shell

ash/wm/video_detector.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 "ash/wm/video_detector.h"
 
 #include "ash/common/wm/window_state.h"
 #include "ash/common/wm_shell.h"
 #include "ash/common/wm_window.h"
 #include "ash/public/cpp/shell_window_ids.h"
@@ skipping 66 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(WindowInfo);
 };
 
 VideoDetector::VideoDetector()
     : state_(State::NOT_PLAYING),
       video_is_playing_(false),
       window_observer_manager_(this),
       is_shutting_down_(false) {
   aura::Env::GetInstance()->AddObserver(this);
-  WmShell::Get()->AddShellObserver(this);
+  Shell::GetInstance()->AddShellObserver(this);
 }
 
 VideoDetector::~VideoDetector() {
-  WmShell::Get()->RemoveShellObserver(this);
+  Shell::GetInstance()->RemoveShellObserver(this);
   aura::Env::GetInstance()->RemoveObserver(this);
 }
 
 void VideoDetector::AddObserver(Observer* observer) {
   observers_.AddObserver(observer);
 }
 
 void VideoDetector::RemoveObserver(Observer* observer) {
   observers_.RemoveObserver(observer);
 }
@@ skipping 89 matching lines @@
   }
 
   if (state_ != new_state) {
     state_ = new_state;
     for (auto& observer : observers_)
       observer.OnVideoStateChanged(state_);
   }
 }
 
 }  // namespace ash