[Media Router WebUI] Use I18nBehavior to retrieve strings.

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

Index: chrome/browser/resources/media_router/elements/media_router_header/media_router_header.js
diff --git a/chrome/browser/resources/media_router/elements/media_router_header/media_router_header.js b/chrome/browser/resources/media_router/elements/media_router_header/media_router_header.js
index 64e324b2a15c33dfc4b60b5551d3b058372126f6..39e00804657b594ea08e7c09be25ae14e7749269 100644
--- a/chrome/browser/resources/media_router/elements/media_router_header/media_router_header.js
+++ b/chrome/browser/resources/media_router/elements/media_router_header/media_router_header.js
@@ -56,27 +56,6 @@ Polymer({
     },
 
     /**
-     * The localized strings used by |this|.
-     * @private {!Object}
-     */
-    i18n_: {
-      readOnly: true,
-      type: Object,
-      value: function() {
-        var strings = {};
-        [
-          'backButtonTitle',
-          'closeButtonTitle',
-          'dropDownButtonTitle',
-        ]
-        .forEach(function(s) {
-          strings[s] = loadTimeData.getString(s);
-        });
-        return strings;
-      },
-    },
-
-    /**
      * Whether to show the user email in the header.
      * @type {boolean}
      */
@@ -115,6 +94,10 @@ Polymer({
     },
   },
 
+  behaviors: [
+    I18nBehavior,
+  ],
+
   ready: function() {
     this.$$('#header').style.height = this.headerWithoutEmailHeight_ + 'px';
   },