Shell of implementation for embedded windows. At this point this is

aura/window_delegate.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_WINDOW_DELEGATE_H_
+#define AURA_WINDOW_DELEGATE_H_
+#pragma once
+
+namespace aura {
+
+// Delegate interface for aura::Window.
+class WindowDelegate {
+ public:
+  // Asks the delegate to paint to the window. The delegate should call back
+  // to the window with SetCanvas.
+  virtual void OnPaint(const gfx::Rect& bounds) = 0;
+
+ protected:
+  virtual ~WindowDelegate() {}
+};
+
+}  // namespace aura
+
+#endif  // AURA_WINDOW_DELEGATE_H_