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..53ca169885bfbe3d826a544dab0e9ac1a2c21287 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_DISABLE_BUTTON" desc="Accessibility role description for media remoting disable button">
+        disable media remoting
+      </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_DISABLE_BUTTON_HELP" desc="Accessibility help description for media remoting disable button">
+        disable media remoting
+      </message>
+
       <message name="IDS_AX_MEDIA_OVERFLOW_BUTTON_HELP" desc="Accessibility help description for overflow button.">
         more options
       </message>