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

content/app/strings/content_strings.grd

Index: content/app/strings/content_strings.grd
diff --git a/content/app/strings/content_strings.grd b/content/app/strings/content_strings.grd
index 36679737ba180cd441ff41c1912fb6c1e1db6281..e8de3de4693ca02bf62dcdfaa80130bb72c43168 100644
--- a/content/app/strings/content_strings.grd
+++ b/content/app/strings/content_strings.grd
@@ -599,6 +599,10 @@ below:
         control remote playback
       </message>
 
+      <message name="IDS_AX_MEDIA_REMOTING_CAST_ICON" desc="Accessibility role description for media remoting cast icon">
+        video is being streamed remotely
+      </message>
+
       <message name="IDS_AX_MEDIA_DOWNLOAD_BUTTON" desc="Media controls download button.">
         download media
       </message>
@@ -679,6 +683,10 @@ below:
         control remote playback
       </message>
 
+      <message name="IDS_AX_MEDIA_REMOTING_CAST_ICON_HELP" desc="Accessibility help description for media remoting disable button">
+        video is being streamed remotely
+      </message>
+
       <message name="IDS_AX_MEDIA_OVERFLOW_BUTTON_HELP" desc="Accessibility help description for overflow button.">
         more options
       </message>
@@ -869,6 +877,12 @@ below:
       <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_CASTING_TEXT" desc="The text is shown when the video is currently being streamed remotely.">
+       Casting Video...
+      </message>
+      <message name="IDS_MEDIA_REMOTING_DISABLE_TEXT" desc="Media remoting disable button label.">
+       Exit
+      </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>