[MediaRouter] Add implementation of PresentationServiceDelegate

chrome/browser/media/router/media_source_helper.cc

Index: chrome/browser/media/router/media_source_helper.cc
diff --git a/chrome/browser/media/router/media_source_helper.cc b/chrome/browser/media/router/media_source_helper.cc
index 305a00fa3437dd83fa5b8eba3de0bdb61e65380c..1db6661a23f0cea16802bbe6380f9081c66b8e91 100644
--- a/chrome/browser/media/router/media_source_helper.cc
+++ b/chrome/browser/media/router/media_source_helper.cc
@@ -26,7 +26,7 @@ MediaSource ForDesktopMediaSource() {
 }
 
 // TODO(mfoltz): Remove when the TODO in
-// MediaSourceManager::GetDefaultMediaSource is resolved.
+// PresentationServiceDelegateImpl::default_source is resolved.
 MediaSource ForCastAppMediaSource(const std::string& app_id) {
   return MediaSource(kCastUrnPrefix + app_id);
 }
@@ -49,4 +49,8 @@ bool IsValidMediaSource(const MediaSource& source) {
   return url.is_valid() && url.SchemeIsHTTPOrHTTPS();
 }
 
+std::string GetPresentationUrl(const MediaSource& source) {
+  return IsValidPresentationUrl(source.id()) ? source.id() : "";
+}
+
 }  // namespace media_router