Implement media Cast button in Blink

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 c62933a9d3a5c805bc3c713658c49be34f8ac6e6..c20bb68e364aeb9edd1b5e1eeaf5c34ae5341f38 100644
--- a/content/app/strings/content_strings.grd
+++ b/content/app/strings/content_strings.grd
@@ -457,6 +457,14 @@ below:
       <message name="IDS_AX_MEDIA_HIDE_CLOSED_CAPTIONS_BUTTON" desc="accessibility role description for hide closed captions button">
         hide closed captions
       </message>
+      
+      <message name="IDS_AX_MEDIA_CAST_OFF_BUTTON" desc="accessibility role description for remote playback button">
+        play on remote device
+      </message>
+      
+      <message name="IDS_AX_MEDIA_CAST_ON_BUTTON" desc="accessibility role description for remote playback control button">
+        control remote playback
+      </message>
 
       <message name="IDS_AX_MEDIA_AUDIO_ELEMENT_HELP" desc="Accessible help of audio controls">
         audio
@@ -518,6 +526,14 @@ below:
         stop displaying closed captions
       </message>
 
+      <message name="IDS_AX_MEDIA_CAST_OFF_BUTTON_HELP" desc="accessibility help description for remote playback button">
+        play on remote device
+      </message>
+      
+      <message name="IDS_AX_MEDIA_CAST_ON_BUTTON_HELP" desc="accessibility help description for remote playback control button">
+        control remote playback
+      </message>
+
       <message name="IDS_AX_MILLISECOND_FIELD_TEXT" desc="Accessible description of the millisecond field in a date/time control">
         Milliseconds
       </message>