Fixes crah in NativeWidgetAura::IsActive()

ui/views/widget/native_widget_aura.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 "ui/views/widget/native_widget_aura.h"
 
 #include "base/bind.h"
 #include "base/strings/string_util.h"
 #include "third_party/skia/include/core/SkRegion.h"
 #include "ui/aura/client/activation_client.h"
@@ skipping 503 matching lines @@
 }
 
 void NativeWidgetAura::Deactivate() {
   if (!window_)
     return;
   aura::client::GetActivationClient(window_->GetRootWindow())->DeactivateWindow(
       window_);
 }
 
 bool NativeWidgetAura::IsActive() const {
-  return window_ &&
-      aura::client::GetActivationClient(window_->GetRootWindow())->
-          GetActiveWindow() == window_;
+  if (!window_)
+    return false;
+
+  // We may up here during destruction of the root, in which case
+  // GetRootWindow() returns NULL (~RootWindow() has run and we're in ~Window).
+  aura::RootWindow* root = window_->GetRootWindow();
+  return root &&
+      aura::client::GetActivationClient(root)->GetActiveWindow() == window_;
 }
 
 void NativeWidgetAura::SetAlwaysOnTop(bool on_top) {
   if (window_)
     window_->SetProperty(aura::client::kAlwaysOnTopKey, on_top);
 }
 
 void NativeWidgetAura::Maximize() {
   if (window_)
     window_->SetProperty(aura::client::kShowStateKey, ui::SHOW_STATE_MAXIMIZED);
@@ skipping 586 matching lines @@
   return aura::Env::GetInstance()->is_mouse_button_down();
 }
 
 // static
 bool NativeWidgetPrivate::IsTouchDown() {
   return aura::Env::GetInstance()->is_touch_down();
 }
 
 }  // namespace internal
 }  // namespace views