[Media Router] Convert MediaRouter to use GURL for presentation URLs.

chrome/browser/media/router/media_source.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_source.h"
 
 #include <string>
 
+#include "url/gurl.h"
+
 namespace media_router {
 
 MediaSource::MediaSource(const MediaSource::Id& source_id) : id_(source_id) {
 }
 
+MediaSource::MediaSource(const GURL& presentation_url)
+    : id_(presentation_url.spec()) {}
+
 MediaSource::~MediaSource() {}
 
 MediaSource::Id MediaSource::id() const {
   return id_;
 }
 
 bool MediaSource::operator==(const MediaSource& other) const {
   return id_ == other.id();
 }
 
 std::string MediaSource::ToString() const {
   return "MediaSource[" + id_ + "]";
 }
 
 }  // namespace media_router