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

ui/keyboard/keyboard_constants.cc

Index: ui/keyboard/keyboard_constants.cc
diff --git a/ui/keyboard/keyboard_switches.cc b/ui/keyboard/keyboard_constants.cc
similarity index 58%
copy from ui/keyboard/keyboard_switches.cc
copy to ui/keyboard/keyboard_constants.cc
index d1ea4e2cbba4b7a9e2f187a17db7664230b35b3a..35f813006339a5a7c861adb7b2db40e3dca44646 100644
--- a/ui/keyboard/keyboard_switches.cc
+++ b/ui/keyboard/keyboard_constants.cc
@@ -2,12 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "ui/keyboard/keyboard_switches.h"
+#include "ui/keyboard/keyboard_constants.h"
 
 namespace keyboard {
-namespace switches {
 
-const char kEnableVirtualKeyboard[] = "enable-virtual-keyboard";
+const char kKeyboardWebUIURL[] = "chrome://keyboard";
+const char kKeyboardWebUIHost[] = "keyboard";
 
-}  // namespace switches
 }  // namespace keyboard