[Media Router] Allow casting new media to sink with existing route.

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

Index: chrome/browser/resources/media_router/elements/route_details/route_details.js
diff --git a/chrome/browser/resources/media_router/elements/route_details/route_details.js b/chrome/browser/resources/media_router/elements/route_details/route_details.js
index d3db440a8042f08e4e0e3d4d2d61e075ae257cf2..3283b0165f2ce63532900b521feca6cfebe67497 100644
--- a/chrome/browser/resources/media_router/elements/route_details/route_details.js
+++ b/chrome/browser/resources/media_router/elements/route_details/route_details.js
@@ -17,6 +17,16 @@ Polymer({
     },
 
     /**
+     * Bitmask of available cast modes compatible with the sink of the current
+     * route.
+     * @type {number}
+     */
+    availableCastModes: {
+      type: Number,
+      value: 0,
+    },
+
+    /**
      * Whether the browser is currently incognito.
      * @type {boolean|undefined}
      */
@@ -60,13 +70,28 @@ Polymer({
   },
 
   /**
-   * Fires a start-casting-to-route-click event. This is called when the button
-   * to start casting to the current route is clicked.
+   * @param {?media_router.Route|undefined} route
+   * @param {number} availableCastModes
+   * @return {boolean} Whether to show the button that allows casting to the
+   *     current route or the current route's sink.
+   */
+  computeCastButtonHidden_: function(route, availableCastModes) {
+    return !(route && route.canJoin) && !availableCastModes;
+  },
+
+  /**
+   * Fires a join-route-click event if the current route is joinable, otherwise
+   * it fires a cast-new-media-click event. This is called when the button to

[apacible, 2016/05/25 22:37:01]

nit: "... a cast-new-media-click event, which stops the current route and
immediately launches a new route to the same sink..." (something like that)

[btolsch, 2016/05/26 00:31:12]

Done.

+   * start casting to the current route is clicked.
    *
    * @private
    */
   startCastingToRoute_: function() {
-    this.fire('start-casting-to-route-click', {route: this.route});
+    if (this.route.canJoin) {
+      this.fire('join-route-click', {route: this.route});
+    } else {
+      this.fire('cast-new-media-click', {route: this.route});

[apacible, 2016/05/25 22:37:01]

What happens if there's already a pending created route in the
media-router-container?

[btolsch, 2016/05/26 00:31:12]

Currently, only the sink for this route would show a spinner and the previously
pending route wouldn't be displayed in route details when it's returned.

If this is undesirable, the container could either do nothing when we get the
event or maybe set availableCastModes to 0 to prevent the cast button from being
shown in route details in the first place.  One problem with the latter option
is that the cast button would still appear and be usable if the route is
joinable.  We could also add or change the parameters of route details to let
the container completely disable the cast button in this case.

+    }
   },
 
   /**