Pass origin to StartObservingMediaSinks.

chrome/test/media_router/test_media_sinks_observer.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <string>
 #include <utility>
 
 #include "chrome/browser/media/router/media_router.h"
 #include "chrome/test/media_router/test_media_sinks_observer.h"
+#include "url/gurl.h"
 
 namespace media_router {
 
 TestMediaSinksObserver::TestMediaSinksObserver(MediaRouter* router,
                                                const MediaSource& source)
     : MediaSinksObserver(router, source) {
 }
 
 TestMediaSinksObserver::~TestMediaSinksObserver() {
 }
 
 void TestMediaSinksObserver::OnSinksReceived(
+    const MediaSource& incomingSource,
     const std::vector<MediaSink>& result) {
+  if (!incomingSource.Equals(source())) {
+    return;
+  }
   sink_map.clear();
   for (const MediaSink& sink : result) {
     sink_map.insert(std::make_pair(sink.name(), sink));
   }
 }
 
 }  // namespace media_router