Added stub MediaSourcePlayer for developing behind the flag

chrome/app/generated_resources.grd

Index: chrome/app/generated_resources.grd
diff --git a/chrome/app/generated_resources.grd b/chrome/app/generated_resources.grd
index 7c366363beda033a3567ddf9d24f57933e052427..6036a3063cf9467c1f10e908f3a5ee4d8878686c 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -6119,6 +6119,12 @@ Keep your key file in a safe place. You will need it to create new versions of y
       <message name="IDS_FLAGS_DISABLE_MEDIA_SOURCE_DESCRIPTION" desc="Description for the flag to disable the Media Source API.">
         Disable the MediaSource object. This object allows JavaScript to send media data directly to a video element.
       </message>
+      <message name="IDS_FLAGS_ENABLE_MEDIA_PLAYER_V2_NAME" desc="Title for the flag to enable the enhanced version of MediaSource player.">
+        Enable MediaSource player version 2.
+      </message>
+      <message name="IDS_FLAGS_ENABLE_MEDIA_PLAYER_V2_DESCRIPTION" desc="Description for the flag to enable the enhanced version of Media Source player.">
+        Use the version of MediaSource player that has a dedicated input thread.
+      </message>
       <message name="IDS_FLAGS_DISABLE_ENCRYPTED_MEDIA_NAME" desc="Title for the flag to disable the Encrypted Media Extensions APIs.">
         Disable Encrypted Media Extensions.
       </message>