aura: Fix segfault when launching aura_demo on Linux.

ui/aura/demo/demo_main.cc

Index: ui/aura/demo/demo_main.cc
diff --git a/ui/aura/demo/demo_main.cc b/ui/aura/demo/demo_main.cc
index be1c68471f7a8877980d84ad926ef604f207bd9e..c6d422f3cb150d0861e39a990702b77146b9b6f3 100644
--- a/ui/aura/demo/demo_main.cc
+++ b/ui/aura/demo/demo_main.cc
@@ -8,6 +8,7 @@
 #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"
@@ -71,6 +72,27 @@ class DemoWindowDelegate : public aura::WindowDelegate {
   DISALLOW_COPY_AND_ASSIGN(DemoWindowDelegate);
 };
 
+class StackingClientImpl : public aura::client::StackingClient {

[Ben Goodger (Google), 2012/03/12 16:35:33]

DemoStackingClient (a la DemoWindowDelegate, above)

[tfarina, 2012/03/12 17:36:04]

Done.

+ public:
+  explicit StackingClientImpl(aura::RootWindow* root_window)
+      : root_window_(root_window) {
+    aura::client::SetStackingClient(this);
+  }
+
+  virtual ~StackingClientImpl() {
+    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(StackingClientImpl);
+};
 
 }  // namespace
 
@@ -89,6 +111,8 @@ int main(int argc, char** argv) {
   ui::CompositorTestSupport::Initialize();
 
   scoped_ptr<aura::RootWindow> root_window(new aura::RootWindow);
+  scoped_ptr<StackingClientImpl> stacking_client(new StackingClientImpl(
+      root_window.get()));
 
   // Create a hierarchy of test windows.
   DemoWindowDelegate window_delegate1(SK_ColorBLUE);