Moves maintaining ShellObservers back to Shell

ash/common/frame/header_view.cc

 // Copyright 2016 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/frame/header_view.h"
 
 #include "ash/common/frame/caption_buttons/frame_caption_button_container_view.h"
 #include "ash/common/frame/default_header_painter.h"
 #include "ash/common/session/session_state_delegate.h"
 #include "ash/common/wm_shell.h"
 #include "ash/common/wm_window.h"
+#include "ash/shell.h"
 #include "ui/gfx/canvas.h"
 #include "ui/views/controls/image_view.h"
 #include "ui/views/widget/widget.h"
 
 namespace ash {
 
 HeaderView::HeaderView(views::Widget* target_widget,
                        mojom::WindowStyle window_style)
     : target_widget_(target_widget),
       header_painter_(base::MakeUnique<DefaultHeaderPainter>(window_style)),
       avatar_icon_(nullptr),
       caption_button_container_(nullptr),
       fullscreen_visible_fraction_(0) {
   caption_button_container_ =
       new FrameCaptionButtonContainerView(target_widget_);
   caption_button_container_->UpdateSizeButtonVisibility();
   AddChildView(caption_button_container_);
 
   header_painter_->Init(target_widget_, this, caption_button_container_);
   UpdateAvatarIcon();
 
-  WmShell::Get()->AddShellObserver(this);
+  Shell::GetInstance()->AddShellObserver(this);
 }
 
 HeaderView::~HeaderView() {
-  WmShell::Get()->RemoveShellObserver(this);
+  Shell::GetInstance()->RemoveShellObserver(this);
 }
 
 void HeaderView::SchedulePaintForTitle() {
   header_painter_->SchedulePaintForTitle();
 }
 
 void HeaderView::ResetWindowControls() {
   caption_button_container_->ResetWindowControls();
 }
 
@@ skipping 145 matching lines @@
   gfx::Rect visible_bounds(GetVisibleBounds());
   gfx::Point visible_origin_in_screen(visible_bounds.origin());
   views::View::ConvertPointToScreen(this, &visible_origin_in_screen);
   std::vector<gfx::Rect> bounds_in_screen;
   bounds_in_screen.push_back(
       gfx::Rect(visible_origin_in_screen, visible_bounds.size()));
   return bounds_in_screen;
 }
 
 }  // namespace ash