mash: Partially migrate WorkspaceController to ash common.

ash/aura/wm_window_aura.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/aura/wm_window_aura.h"
 
 #include "ash/aura/aura_layout_manager_adapter.h"
 #include "ash/aura/wm_root_window_controller_aura.h"
 #include "ash/aura/wm_shell_aura.h"
 #include "ash/common/ash_constants.h"
@@ skipping 337 matching lines @@
 }
 
 std::vector<WmWindow*> WmWindowAura::GetTransientChildren() {
   return FromAuraWindows(::wm::GetTransientChildren(window_));
 }
 
 void WmWindowAura::SetLayoutManager(
     std::unique_ptr<WmLayoutManager> layout_manager) {
   // |window_| takes ownership of AuraLayoutManagerAdapter.
   window_->SetLayoutManager(
-      new AuraLayoutManagerAdapter(std::move(layout_manager)));
+      layout_manager ? new AuraLayoutManagerAdapter(std::move(layout_manager))
+                     : nullptr);
 }
 
 WmLayoutManager* WmWindowAura::GetLayoutManager() {
-  return static_cast<AuraLayoutManagerAdapter*>(window_->layout_manager())
-      ->wm_layout_manager();
+  AuraLayoutManagerAdapter* adapter =
+      static_cast<AuraLayoutManagerAdapter*>(window_->layout_manager());
+  return adapter ? adapter->wm_layout_manager() : nullptr;
 }
 
 void WmWindowAura::SetVisibilityAnimationType(int type) {
   ::wm::SetWindowVisibilityAnimationType(window_, type);
 }
 
 void WmWindowAura::SetVisibilityAnimationDuration(base::TimeDelta delta) {
   ::wm::SetWindowVisibilityAnimationDuration(window_, delta);
 }
 
@@ skipping 448 matching lines @@
                     OnTransientChildAdded(this, Get(transient)));
 }
 
 void WmWindowAura::OnTransientChildRemoved(aura::Window* window,
                                            aura::Window* transient) {
   FOR_EACH_OBSERVER(WmTransientWindowObserver, transient_observers_,
                     OnTransientChildRemoved(this, Get(transient)));
 }
 
 }  // namespace ash