Fix WindowTreeHostManager::GetPrimaryRootWindow.

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 <vector>
 
 #include "ash/ash_constants.h"
 #include "ash/root_window_controller.h"
@@ skipping 45 matching lines @@
 }
 
 void DeactivateWindow(aura::Window* window) {
   ::wm::DeactivateWindow(window);
 }
 
 bool IsActiveWindow(aura::Window* window) {
   return ::wm::IsActiveWindow(window);
 }
 
 aura::Window* GetActiveWindow() {

[varkha, 2017/05/10 22:23:59]

nit: Maybe a comment about when primary root window might be null.

-  return aura::client::GetActivationClient(Shell::GetPrimaryRootWindow())
-      ->GetActiveWindow();
+  auto* client =
+      aura::client::GetActivationClient(Shell::GetPrimaryRootWindow());
+  return client ? client->GetActiveWindow() : nullptr;
 }
 
 aura::Window* GetActivatableWindow(aura::Window* window) {
   return ::wm::GetActivatableWindow(window);
 }
 
 bool CanActivateWindow(aura::Window* window) {
   return ::wm::CanActivateWindow(window);
 }
 
@@ skipping 51 matching lines @@
 }
 
 void SetSnapsChildrenToPhysicalPixelBoundary(aura::Window* container) {
   DCHECK(!container->GetProperty(kSnapChildrenToPixelBoundary))
       << container->GetName();
   container->SetProperty(kSnapChildrenToPixelBoundary, true);
 }
 
 }  // namespace wm
 }  // namespace ash