[Media Router] Use correct Mojo object name in media_router_bindings

We recently renamed mediaRouterMojom to mediaRouter.mojom in media_router_bindings.js, so use of the former gives an error.

Bug: 792125
Change-Id: I36c35c67cbd39a684bbe61de1b4c72b67df95bc9
Reviewed-on: https://chromium-review.googlesource.com/809465Reviewed-by: Derek Cheng <imcheng@chromium.org>
Commit-Queue: Takumi Fujimoto <takumif@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521763}

chrome/renderer/resources/extensions/media_router_bindings.js

@@ -497,7 +497,7 @@ function sinkToMojo_(sink) {
     'domain': sink.domain,
     'sinkId': sink.id,
     'iconType': sinkIconTypeToMojo(sink.iconType),
-    'provider_id': mediaRouterMojom.MediaRouteProvider.Id.EXTENSION,
+    'provider_id': mediaRouter.mojom.MediaRouteProvider.Id.EXTENSION,
   });
 }