Moves maintaining ShellObservers back to Shell

ash/mus/bridge/wm_shell_mus.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/mus/bridge/wm_shell_mus.h"
 
 #include <utility>
 
 #include "ash/common/accelerators/accelerator_controller.h"
 #include "ash/common/key_event_watcher.h"
@@ skipping 340 matching lines @@
 WmShellMus::CreateImmersiveFullscreenController() {
   return base::MakeUnique<ImmersiveFullscreenController>();
 }
 
 std::unique_ptr<KeyEventWatcher> WmShellMus::CreateKeyEventWatcher() {
   // TODO: needs implementation for mus, http://crbug.com/649600.
   NOTIMPLEMENTED();
   return std::unique_ptr<KeyEventWatcher>();
 }
 
-void WmShellMus::OnOverviewModeStarting() {
-  for (auto& observer : *shell_observers())
-    observer.OnOverviewModeStarting();
-}
-
-void WmShellMus::OnOverviewModeEnded() {
-  for (auto& observer : *shell_observers())
-    observer.OnOverviewModeEnded();
-}
-
 SessionStateDelegate* WmShellMus::GetSessionStateDelegate() {
   return session_state_delegate_
              ? session_state_delegate_.get()
              : Shell::GetInstance()->session_state_delegate();
 }
 
 void WmShellMus::AddDisplayObserver(WmDisplayObserver* observer) {
   NOTIMPLEMENTED();
 }
 
@@ skipping 36 matching lines @@
 }
 
 void WmShellMus::CreatePrimaryHost() {}
 
 void WmShellMus::InitHosts(const ShellInitParams& init_params) {
   window_manager_->CreatePrimaryRootWindowController(
       base::WrapUnique(init_params.primary_window_tree_host));
 }
 }  // namespace mus
 }  // namespace ash