Moves maintaining ShellObservers back to Shell

ash/common/wm/panels/panel_layout_manager.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/panels/panel_layout_manager.h"
 
 #include <algorithm>
 #include <map>
 #include <utility>
 
@@ skipping 235 matching lines @@
       in_layout_(false),
       show_callout_widgets_(true),
       dragged_panel_(NULL),
       shelf_(nullptr),
       last_active_panel_(NULL),
       weak_factory_(this) {
   DCHECK(panel_container);
   WmShell* shell = panel_container->GetShell();
   Shell::GetInstance()->activation_client()->AddObserver(this);
   shell->AddDisplayObserver(this);
-  shell->AddShellObserver(this);
+  Shell::GetInstance()->AddShellObserver(this);
 }
 
 PanelLayoutManager::~PanelLayoutManager() {
   Shutdown();
 }
 
 // static
 PanelLayoutManager* PanelLayoutManager::Get(WmWindow* window) {
   if (!window)
     return nullptr;
@@ skipping 10 matching lines @@
     shelf_ = nullptr;
   }
   for (PanelList::iterator iter = panel_windows_.begin();
        iter != panel_windows_.end(); ++iter) {
     delete iter->callout_widget;
   }
   panel_windows_.clear();
   WmShell* shell = panel_container_->GetShell();
   Shell::GetInstance()->activation_client()->RemoveObserver(this);
   shell->RemoveDisplayObserver(this);
-  shell->RemoveShellObserver(this);
+  Shell::GetInstance()->RemoveShellObserver(this);
 }
 
 void PanelLayoutManager::StartDragging(WmWindow* panel) {
   DCHECK(!dragged_panel_);
   dragged_panel_ = panel;
   Relayout();
 }
 
 void PanelLayoutManager::FinishDragging() {
   dragged_panel_ = NULL;
@@ skipping 627 matching lines @@
     }
   }
   // This bounds change will have caused a change to the Shelf which does not
   // propogate automatically to this class, so manually recalculate bounds.
   OnWindowResized();
 }
 
 void PanelLayoutManager::OnKeyboardClosed() {}
 
 }  // namespace ash