[Media Router] Conditionally enable mDNS on Windows.

chrome/browser/media/router/media_router.h

Index: chrome/browser/media/router/media_router.h
diff --git a/chrome/browser/media/router/media_router.h b/chrome/browser/media/router/media_router.h
index d932d9330a0d0469a057d29fe4bddcca1d4a315d..c7b68d4dc7260a8a53c1604404ef71a59b456c84 100644
--- a/chrome/browser/media/router/media_router.h
+++ b/chrome/browser/media/router/media_router.h
@@ -154,6 +154,11 @@ class MediaRouter : public KeyedService {
   // Clears the issue with the id |issue_id|.
   virtual void ClearIssue(const Issue::Id& issue_id) = 0;
 
+  // Notifies the Media Router that the user has taken an action involving the
+  // Media Router. This can be used to perform any initialization that is not
+  // approriate to be done at construction.
+  virtual void OnUserGesture() = 0;
+
   // Adds |callback| to listen for state changes for presentation connected to
   // |route_id|. The returned Subscription object is owned by the caller.
   // |callback| will be invoked whenever there are state changes, until the