aura: A few changes to have aura_demo compile and run on linux.

aura/desktop.h

 // Copyright (c) 2011 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.
 
 #ifndef AURA_DESKTOP_H_
 #define AURA_DESKTOP_H_
 #pragma once
 
 #include "aura/root_window.h"
+#include "aura/aura_export.h"
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "ui/gfx/native_widget_types.h"
 
 namespace gfx {
 class Size;
 }
 
 namespace ui {
 class Compositor;
 }
 
 namespace aura {
 
 class DesktopHost;
 class MouseEvent;
 
 // Desktop is responsible for hosting a set of windows.
-class Desktop {
+class AURA_EXPORT Desktop {
  public:
   Desktop();
   ~Desktop();
 
   // Shows the desktop host.
   void Show();
 
   // Sets the size of the desktop.
   void SetSize(const gfx::Size& size);
 
@@ skipping 24 matching lines @@
   DesktopHost* host_;
 
   static Desktop* instance_;
 
   DISALLOW_COPY_AND_ASSIGN(Desktop);
 };
 
 }  // namespace aura
 
 #endif  // AURA_DESKTOP_H_