Moves maintaining ShellObservers back to Shell

ash/common/wm/maximize_mode/maximize_mode_window_manager.cc

 // Copyright 2014 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/maximize_mode/maximize_mode_window_manager.h"
 
 #include "ash/common/ash_switches.h"
 #include "ash/common/session/session_state_delegate.h"
 #include "ash/common/wm/maximize_mode/maximize_mode_event_handler.h"
 #include "ash/common/wm/maximize_mode/maximize_mode_window_state.h"
@@ skipping 30 matching lines @@
 }  // namespace
 
 MaximizeModeWindowManager::~MaximizeModeWindowManager() {
   // Overview mode needs to be ended before exiting maximize mode to prevent
   // transforming windows which are currently in
   // overview: http://crbug.com/366605
   CancelOverview();
   for (aura::Window* window : added_windows_)
     window->RemoveObserver(this);
   added_windows_.clear();
-  WmShell::Get()->RemoveShellObserver(this);
+  Shell::GetInstance()->RemoveShellObserver(this);
   display::Screen::GetScreen()->RemoveObserver(this);
   EnableBackdropBehindTopWindowOnEachDisplay(false);
   RemoveWindowCreationObservers();
   RestoreAllWindows();
 }
 
 int MaximizeModeWindowManager::GetNumberOfManagedWindows() {
   return window_state_map_.size();
 }
 
@@ skipping 137 matching lines @@
 MaximizeModeWindowManager::MaximizeModeWindowManager()
     : backdrops_hidden_(false) {
   // The overview mode needs to be ended before the maximize mode is started. To
   // guarantee the proper order, it will be turned off from here.
   CancelOverview();
 
   MaximizeAllWindows();
   AddWindowCreationObservers();
   EnableBackdropBehindTopWindowOnEachDisplay(true);
   display::Screen::GetScreen()->AddObserver(this);
-  WmShell::Get()->AddShellObserver(this);
+  Shell::GetInstance()->AddShellObserver(this);
   event_handler_ = WmShell::Get()->CreateMaximizeModeEventHandler();
 }
 
 void MaximizeModeWindowManager::MaximizeAllWindows() {
   MruWindowTracker::WindowList windows =
       WmShell::Get()->mru_window_tracker()->BuildWindowListIgnoreModal();
   // Add all existing Mru windows.
   for (WmWindow* window : windows)
     MaximizeAndTrackWindow(window);
 }
@@ skipping 103 matching lines @@
     RootWindowController* controller = root->GetRootWindowController();
     WmWindow* default_container =
         root->GetChildByShellWindowId(kShellWindowId_DefaultContainer);
     controller->workspace_controller()->SetMaximizeBackdropDelegate(
         enable ? base::MakeUnique<WorkspaceBackdropDelegate>(default_container)
                : nullptr);
   }
 }
 
 }  // namespace ash