[Media Router] Add Media Router Mojo impl code.

chrome/browser/media/router/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 "chrome/browser/media/router/media_sinks_observer.h"
 
 #include "base/logging.h"
 #include "chrome/browser/media/router/media_router.h"
 
 namespace media_router {
 
 MediaSinksObserver::MediaSinksObserver(MediaRouter* router,
                                        const MediaSource& source)
     : source_(source), router_(router) {
   DCHECK(router_);
-  if (!router_->RegisterMediaSinksObserver(this))
-    LOG(ERROR) << "RegisterMediaSinksObserver failed: " << source.ToString();
+  router_->RegisterMediaSinksObserver(this);
 }
 
 MediaSinksObserver::~MediaSinksObserver() {
   router_->UnregisterMediaSinksObserver(this);
 }
 
 }  // namespace media_router