MediaRouter: Fix comment

Change-Id: I3c6104ecf00918ba689b1d6a6d141c70c0422e43
diff --git a/v7/mediarouter/src/android/support/v7/app/MediaRouteControllerDialog.java b/v7/mediarouter/src/android/support/v7/app/MediaRouteControllerDialog.java
index 4ca7f74..69132d8 100644
--- a/v7/mediarouter/src/android/support/v7/app/MediaRouteControllerDialog.java
+++ b/v7/mediarouter/src/android/support/v7/app/MediaRouteControllerDialog.java
@@ -257,9 +257,9 @@
     }
 
     /**
-     * Gets the associated session's token.
+     * Gets the session to use for metadata and transport controls.
      *
-     * @return session token.
+     * @return The token for the session to use or null if none.
      */
     public MediaSessionCompat.Token getMediaSession() {
         return mMediaController == null ? null : mMediaController.getSessionToken();