Add initial home card impl.

athena/screen/public/screen_manager.h

 // Copyright 2014 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 ATHENA_SCREEN_PUBLIC_SCREEN_MANAGER_H_
 #define ATHENA_SCREEN_PUBLIC_SCREEN_MANAGER_H_
 
+#include <string>
+
 #include "athena/athena_export.h"
 
 namespace aura {
 class Window;
 }
 
 namespace gfx {
 class ImageSkia;
 }
 
 namespace athena {
 
-// Mananges screen and UI components on the screen such as background,
-// home card, etc.
+// Mananges basic UI components on the screen such as background, and provide
+// API for other UI components, such as window manager, home card, to
+// create and manage their windows on the screen.
 class ATHENA_EXPORT ScreenManager {
  public:
   // Creates, returns and deletes the singleton object of the ScreenManager
   // implementation.
   static ScreenManager* Create(aura::Window* root);
   static ScreenManager* Get();
   static void Shutdown();
 
   virtual ~ScreenManager() {}
 
-  // Returns the container window for window on the screen.
-  virtual aura::Window* GetContainerWindow() = 0;
+  // Creates the container window that is used when creating a normal
+  // widget without specific parent.
+  virtual aura::Window* CreateDefaultContainer(const std::string& name) = 0;
+
+  // Creates the container window on the screen.
+  virtual aura::Window* CreateContainer(const std::string& name) = 0;
 
   // Return the context object to be used for widget creation.
   virtual aura::Window* GetContext() = 0;
 
   // Sets the background image.
   virtual void SetBackgroundImage(const gfx::ImageSkia& image) = 0;
 };
 
 }  // namespace athena
 
 #endif  // ATHENA_SCREEN_PUBLIC_SCREEN_MANAGER_H_