Revert r128507 "Revert r128436 "relanding: disabled workspace_window_resizer test. fixed access-aft…

ash/wm/window_util.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/wm/window_util.h"
 
 #include "ash/shell.h"
 #include "ash/wm/activation_controller.h"
 #include "ui/aura/client/activation_client.h"
 #include "ui/aura/client/aura_constants.h"
@@ skipping 21 matching lines @@
   DCHECK(window);
   DCHECK(window->GetRootWindow());
   aura::client::GetActivationClient(window->GetRootWindow())->DeactivateWindow(
       window);
 }
 
 bool IsActiveWindow(aura::Window* window) {
   DCHECK(window);
   if (!window->GetRootWindow())
     return false;
-
-  return aura::client::GetActivationClient(window->GetRootWindow())->
-      GetActiveWindow() == window;
+  aura::client::ActivationClient* client =
+      aura::client::GetActivationClient(window->GetRootWindow());
+  return client && client->GetActiveWindow() == window;
 }
 
 aura::Window* GetActiveWindow() {
   return aura::client::GetActivationClient(Shell::GetRootWindow())->
       GetActiveWindow();
 }
 
 aura::Window* GetActivatableWindow(aura::Window* window) {
   return internal::ActivationController::GetActivatableWindow(window, NULL);
 }
@@ skipping 31 matching lines @@
 void SetOpenWindowSplit(aura::Window* window, bool value) {
   window->SetProperty(kOpenWindowSplitKey, value);
 }
 
 bool GetOpenWindowSplit(aura::Window* window) {
   return window->GetProperty(kOpenWindowSplitKey);
 }
 
 }  // namespace wm
 }  // namespace ash