aura: Fix segfault when launching aura_demo on Linux.

ui/aura/demo/demo_main.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 "base/at_exit.h"
 #include "base/command_line.h"
 #include "base/i18n/icu_util.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/message_loop.h"
 #include "third_party/skia/include/core/SkXfermode.h"
+#include "ui/aura/client/stacking_client.h"
 #include "ui/aura/event.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_delegate.h"
 #include "ui/base/hit_test.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/aura/root_window.h"
 #include "ui/base/ui_base_paths.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/compositor/test/compositor_test_support.h"
 #include "ui/gfx/rect.h"
@@ skipping 43 matching lines @@
   virtual void OnWindowDestroying() OVERRIDE {}
   virtual void OnWindowDestroyed() OVERRIDE {}
   virtual void OnWindowVisibilityChanged(bool visible) OVERRIDE {}
 
  private:
   SkColor color_;
 
   DISALLOW_COPY_AND_ASSIGN(DemoWindowDelegate);
 };
 
+class DemoStackingClient : public aura::client::StackingClient {
+ public:
+  explicit DemoStackingClient(aura::RootWindow* root_window)
+      : root_window_(root_window) {
+    aura::client::SetStackingClient(this);
+  }
+
+  virtual ~DemoStackingClient() {
+    aura::client::SetStackingClient(NULL);
+  }
+
+  // Overridden from aura::client::StackingClient:
+  virtual aura::Window* GetDefaultParent(aura::Window* window) OVERRIDE {
+    return root_window_;
+  }
+
+ private:
+  aura::RootWindow* root_window_;
+
+  DISALLOW_COPY_AND_ASSIGN(DemoStackingClient);
+};
 
 }  // namespace
 
 int main(int argc, char** argv) {
   CommandLine::Init(argc, argv);
 
   // The exit manager is in charge of calling the dtors of singleton objects.
   base::AtExitManager exit_manager;
 
   ui::RegisterPathProvider();
   icu_util::Initialize();
   ResourceBundle::InitSharedInstanceWithLocale("en-US");
 
   // Create the message-loop here before creating the root window.
   MessageLoop message_loop(MessageLoop::TYPE_UI);
   ui::CompositorTestSupport::Initialize();
 
   scoped_ptr<aura::RootWindow> root_window(new aura::RootWindow);
+  scoped_ptr<DemoStackingClient> stacking_client(new DemoStackingClient(
+      root_window.get()));
 
   // Create a hierarchy of test windows.
   DemoWindowDelegate window_delegate1(SK_ColorBLUE);
   aura::Window window1(&window_delegate1);
   window1.set_id(1);
   window1.Init(ui::Layer::LAYER_TEXTURED);
   window1.SetBounds(gfx::Rect(100, 100, 400, 400));
   window1.Show();
   window1.SetParent(NULL);
 
@@ skipping 13 matching lines @@
   window3.Show();
   window3.SetParent(&window2);
 
   root_window->ShowRootWindow();
   MessageLoopForUI::current()->Run();
 
   ui::CompositorTestSupport::Terminate();
 
   return 0;
 }