[Media Router] Make per-hostname cast mode selections persist

chrome/browser/resources/media_router/elements/media_router_container/media_router_container.js

Index: chrome/browser/resources/media_router/elements/media_router_container/media_router_container.js
diff --git a/chrome/browser/resources/media_router/elements/media_router_container/media_router_container.js b/chrome/browser/resources/media_router/elements/media_router_container/media_router_container.js
index 9e149ca7aadec32a7cad87d47b20e35c48e610cd..5c84497102ef14c342856f8db571a8abde88c4b7 100644
--- a/chrome/browser/resources/media_router/elements/media_router_container/media_router_container.js
+++ b/chrome/browser/resources/media_router/elements/media_router_container/media_router_container.js
@@ -2122,6 +2122,20 @@ Polymer({
   },
 
   /**
+   * Sets the selected cast mode to the one associated with |castModeType|,
+   * and rebuilds sinks to reflect the change.
+   * @param {number} castModeType The type of the initial cast mode.
+   */
+  setInitialCastMode: function(castModeType) {
+    var initialCastMode = this.findCastModeByType_(castModeType);
+    if (initialCastMode) {
+      this.setShownCastMode_(initialCastMode);
+      this.userHasSelectedCastMode_ = true;
+      this.rebuildSinksToShow_();
+    }
+  },
+
+  /**
    * Sets various focus and blur event handlers to handle showing search results
    * when the search input is focused.
    * @private