Implement overscroll support for the virtual keyboard.

ui/aura/client/virtual_keyboard_client.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_CLIENT_H_
+#define UI_AURA_CLIENT_VIRTUAL_KEYBOARD_CLIENT_H_
+
+#include "ui/aura/aura_export.h"
+
+namespace ui {
+class Event;
+}
+
+namespace aura {
+
+class Window;
+
+namespace client {
+class VirtualKeyboardObserver;
+
+// An interface implemented by an object that manages window focus.
+class AURA_EXPORT VirtualKeyboardClient {

[sadrul, 2014/03/26 17:19:18]

Why do we need to introduce this client, and add the observer to this? Why not
continue to use the KeyboardControllerObserver?

[kevers, 2014/03/26 17:43:46]

RWHVA implements several observers in aura::client.  The refactor is to improve
consistency with other observers. If RWHVA directly implements
KeyboardControllerObserver, we need to include the keyboard code on non-ChromeOS
builds.  Adding the client isolates the keyboard implementation, as the
GetVKClient call will simply return NULL on non-ChromeOS builds. 

[sadrul, 2014/03/26 18:26:21]

I don't think adding a new aura-client interface is the solution for that. You
can make RWHVA a KCObserver conditionally on OS_CHROMEOS if including keyboard
code in non-chromeos is a concern. But all the v-keyboard code is built on all
aura platforms anyway. Why does this need to be different?

[kevers, 2014/04/09 20:06:28]

Removed.  Now using singleton keyboard controller.

+ public:
+  virtual ~VirtualKeyboardClient() {}
+
+  virtual void AddObserver(VirtualKeyboardObserver* observer) = 0;
+  virtual void RemoveObserver(VirtualKeyboardObserver* observer) = 0;
+
+  // Returns TRUE if keyboard overscroll mode is enabled.
+  virtual bool IsOverscrollEnabled() = 0;
+};
+
+// Sets/Gets the virtual keyboard client on the root Window.
+AURA_EXPORT void SetVirtualKeyboardClient(Window* root_window,
+                                          VirtualKeyboardClient* client);
+AURA_EXPORT VirtualKeyboardClient* GetVirtualKeyboardClient(
+    const Window* window);
+
+}  // namespace clients
+}  // namespace aura
+
+#endif  // UI_AURA_CLIENT_VIRTUAL_KEYBOARD_CLIENT_H_