Add a virtual keyboard webui at chrome://keyboard/

ui/keyboard/keyboard_constants.h

Index: ui/keyboard/keyboard_constants.h
diff --git a/ui/keyboard/keyboard_constants.h b/ui/keyboard/keyboard_constants.h
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index 0000000000000000000000000000000000000000..eff96eadf5054ae73faf3bca489a703efaf53647
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+++ b/ui/keyboard/keyboard_constants.h
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+// Copyright (c) 2013 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_KEYBOARD_KEYBOARD_CONSTANTS_H_
+#define UI_KEYBOARD_KEYBOARD_CONSTANTS_H_
+
+#include "ui/keyboard/keyboard_export.h"
+
+namespace keyboard {
+
+// The URL of the keyboard WebUI.
+KEYBOARD_EXPORT extern const char kKeyboardWebUIURL[];
+
+// The host of the keyboard WebUI URL.
+KEYBOARD_EXPORT extern const char kKeyboardWebUIHost[];
+
+}  // namespace keyboard
+
+#endif  //  UI_KEYBOARD_KEYBOARD_CONSTANTS_H_