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

chrome/browser/media/router/mock_screen_availability_listener.cc

Index: chrome/browser/media/router/mock_screen_availability_listener.cc
diff --git a/chrome/browser/media/router/mock_screen_availability_listener.cc b/chrome/browser/media/router/mock_screen_availability_listener.cc
index 99f3d32a7512266c715f6cc77bae60f29c1a706e..c2cd512020d96eb8a9cc9058f4fb2804fd673465 100644
--- a/chrome/browser/media/router/mock_screen_availability_listener.cc
+++ b/chrome/browser/media/router/mock_screen_availability_listener.cc
@@ -7,14 +7,13 @@
 namespace media_router {
 
 MockScreenAvailabilityListener::MockScreenAvailabilityListener(
-    const std::string& availability_url)
-    : availability_url_(availability_url) {
-}
+    const GURL& availability_url)
+    : availability_url_(availability_url) {}
 
 MockScreenAvailabilityListener::~MockScreenAvailabilityListener() {
 }
 
-std::string MockScreenAvailabilityListener::GetAvailabilityUrl() const {
+GURL MockScreenAvailabilityListener::GetAvailabilityUrl() const {
   return availability_url_;
 }