Fix the content_browsertests everywhere maybe.

ui/aura/window.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/aura/window.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
@@ skipping 302 matching lines @@
         WindowObserver, observers_, OnWindowPaintScheduled(this, rect));
   }
 }
 
 void Window::SetExternalTexture(ui::Texture* texture) {
   layer_->SetExternalTexture(texture);
 }
 
 void Window::SetDefaultParentByRootWindow(RootWindow* root_window,
                                           const gfx::Rect& bounds_in_screen) {
-  // TODO(erg): Enable this DCHECK once it is safe.
-  //  DCHECK(root_window);
+  DCHECK(root_window);
 
   // Stacking clients are mandatory on RootWindow objects.
   client::StackingClient* client = client::GetStackingClient(root_window);
   DCHECK(client);
 
   aura::Window* default_parent = client->GetDefaultParent(
       root_window, this, bounds_in_screen);
   default_parent->AddChild(this);
 }
 
@@ skipping 631 matching lines @@
   bool contains_mouse = false;
   if (IsVisible()) {
     RootWindow* root_window = GetRootWindow();
     contains_mouse = root_window &&
         ContainsPointInRoot(root_window->GetLastMouseLocationInRoot());
   }
   return contains_mouse;
 }
 
 }  // namespace aura