Add a menu option for the right-hand Ctrl -> Meta mapping.

remoting/webapp/crd/html/window_frame.html

 <!--
 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.
 -->
 <div id="title-bar" class="title-bar apps-v2-only">
   <div class="window-controls-and-title">
     <span i18n-title="OPTIONS_MENU"
           class="window-control window-options menu-button">
       <span class="menu-button-activator">
         <img src="icon_options.webp">
       </span>
       <ul class="window-options-menu right-align">
         <li class="menu-start-stop-recording"
             i18n-content="START_RECORDING"
             hidden></li>
         <li class="menu-send-ctrl-alt-del"
             i18n-content="SEND_CTRL_ALT_DEL"></li>
         <li class="menu-send-print-screen"
             i18n-content="SEND_PRINT_SCREEN"></li>
+        <li class="menu-map-right-ctrl-to-meta"
+            i18n-content="MAP_RIGHT_CTRL_TO_META"></li>
         <li class="menu-separator"></li>
         <li class="menu-resize-to-client"
             i18n-content="RESIZE_TO_CLIENT"></li>
         <li class="menu-shrink-to-fit"
             i18n-content="SHRINK_TO_FIT"></li>
         <li class="menu-separator"></li>
         <li class="menu-new-connection"
             i18n-content="NEW_CONNECTION"></li>
         <li class="menu-separator"></li>
         <li class="menu-toggle-connection-stats"
@@ skipping 21 matching lines @@
           class="window-control window-fullscreen">
       <img src="icon_fullscreen.webp">
     </span>
     <span i18n-title="CLOSE_WINDOW"
           class="window-control window-close">
       <img src="icon_close.webp">
     </span>
   </div>
   <div class="window-controls-stub">&nbsp;</div>
 </div>  <!-- title-bar -->