Implement overscroll support for the virtual keyboard.

ui/aura/client/virtual_keyboard_observer.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 UI_AURA_CLIENT_VIRTUAL_KEYBOARD_OBSERVER_H_
+#define UI_AURA_CLIENT_VIRTUAL_KEYBOARD_OBSERVER_H_
+
+#include "ui/aura/aura_export.h"
+
+namespace gfx {
+class Rect;
+}
+
+namespace aura {
+namespace client {
+
+class AURA_EXPORT VirtualKeyboardObserver {
+ public:
+  virtual void OnKeyboardBoundsChanging(const gfx::Rect& new_bounds) = 0;
+
+ protected:
+  virtual ~VirtualKeyboardObserver() {}
+};
+
+}  // namespace client
+}  // namespace aura
+
+#endif  // UI_AURA_CLIENT_VIRTUAL_KEYBOARD_OBSERVER_H_