Media Remoting: Add interstitial elements to media element shadow dom.

content/app/strings/content_strings.grd

 <?xml version="1.0" encoding="UTF-8"?>
 
 <!-- This file contains definitions of resources that will be translated for
 each locale. Specifically, these are UI strings that are used by content that
 need to be translated for each locale.-->
 
 <!-- Some of these strings and string descriptions were taken from
 WebKit/win/WebCoreLocalizedStrings.cpp so we include the original license
 below:
 
@@ skipping 499 matching lines @@
         <message name="IDS_AX_ROLE_TREE" desc="Accessibility role description for a tree">
           tree
         </message>
         <message name="IDS_AX_ROLE_TREE_GRID" desc="Accessibility role description for a tree grid">
           tree grid
         </message>
         <message name="IDS_AX_ROLE_TREE_ITEM" desc="Accessibility role description for a tree item">
           tree item
         </message>
       </if>
-      
+
       <message name="IDS_AX_AM_PM_FIELD_TEXT" desc="Accessible description of the AM/PM field in a date/time control">
         AM/PM
       </message>
 
       <message name="IDS_AX_DAY_OF_MONTH_FIELD_TEXT" desc="Accessible description of the day of month field in a date/time control">
         Day
       </message>
 
       <message name="IDS_AX_HOUR_FIELD_TEXT" desc="Accessible description of the hour field in a date/time control">
         Hours
@@ skipping 334 matching lines @@
       </message>
       <message name="IDS_MEDIA_OVERFLOW_MENU_PLAY" desc="Media controls overflow menu item label for a play button.">
         Play
       </message>
       <message name="IDS_MEDIA_OVERFLOW_MENU_PAUSE" desc="Media controls overflow menu item label for a pause button.">
         Pause
       </message>
       <message name="IDS_MEDIA_OVERFLOW_MENU_DOWNLOAD" desc="Media controls overflow menu item label for a download button.">
        Download
       </message>
+      <message name="IDS_MEDIA_REMOTING_DISABLE_TEXT" desc="Media remoting disable button label.">
+       Play on both screens
+      </message>
+      <message name="IDS_MEDIA_REMOTING_CAST_TEXT" desc="Media remoting cast video text message.">
+       Now casting to your TV
+      </message>
       <message name="IDS_MEDIA_TRACKS_NO_LABEL" desc="Menu item label for a text track that has no name specified. The number represents the track number in the list of tracks.">
         Track <ph name="NUMBER">$1<ex>1</ex></ph>
       </message>
 
       <message name="IDS_MEDIA_TRACKS_OFF" desc="Menu item label for a text track that represents disabling closed captions">
         Off
       </message>
 
       <message name="IDS_PLUGIN_INITIALIZATION_ERROR" desc="A message displayed when a plugin failed to load">
         Couldn't load plugin.
       </message>
 
     </messages>
   </release>
 </grit>