Moves maintaining ShellObservers back to Shell

ash/common/wm/screen_dimmer.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/common/wm/screen_dimmer.h"
 
 #include "ash/common/wm/container_finder.h"
 #include "ash/common/wm/window_dimmer.h"
 #include "ash/common/wm_shell.h"
 #include "ash/common/wm_window.h"
 #include "ash/common/wm_window_user_data.h"
 #include "ash/public/cpp/shell_window_ids.h"
+#include "ash/shell.h"
 #include "base/memory/ptr_util.h"
 
 namespace ash {
 namespace {
 
 // Opacity when it's dimming the entire screen.
 const float kDimmingLayerOpacityForRoot = 0.4f;
 
 // Opacity for lock screen.
 const float kDimmingLayerOpacityForLockScreen = 0.5f;
 
 }  // namespace
 
 ScreenDimmer::ScreenDimmer(Container container)
     : container_(container),
       is_dimming_(false),
       at_bottom_(false),
       window_dimmers_(base::MakeUnique<WmWindowUserData<WindowDimmer>>()) {
-  WmShell::Get()->AddShellObserver(this);
+  Shell::GetInstance()->AddShellObserver(this);
 }
 
 ScreenDimmer::~ScreenDimmer() {
   // Usage in chrome results in ScreenDimmer outliving the shell.
-  if (WmShell::HasInstance())
-    WmShell::Get()->RemoveShellObserver(this);
+  if (Shell::HasInstance())
+    Shell::GetInstance()->RemoveShellObserver(this);
 }
 
 void ScreenDimmer::SetDimming(bool should_dim) {
   if (should_dim == is_dimming_)
     return;
   is_dimming_ = should_dim;
 
   Update(should_dim);
 }
 
@@ skipping 25 matching lines @@
       else
         container->StackChildAtTop(window_dimmer->window());
       window_dimmer->window()->Show();
     } else if (window_dimmer) {
       window_dimmers_->Set(container, nullptr);
     }
   }
 }
 
 }  // namespace ash