[Media Router] Conditionally enable mDNS on Windows.

chrome/browser/media/router/media_router.h

 // 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.
 
 #ifndef CHROME_BROWSER_MEDIA_ROUTER_MEDIA_ROUTER_H_
 #define CHROME_BROWSER_MEDIA_ROUTER_MEDIA_ROUTER_H_
 
 #include <stdint.h>
 
 #include <string>
@@ skipping 136 matching lines @@
       const MediaRoute::Id& route_id,
       scoped_ptr<std::vector<uint8_t>> data,
       const SendRouteMessageCallback& callback) = 0;
 
   // Adds a new |issue|.
   virtual void AddIssue(const Issue& issue) = 0;
 
   // 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 OnUserInteraction() = 0;

[mark a. foltz, 2016/03/29 00:48:20]

Sorry to bikeshed, but often user initiated actions on the Web are called "user
gestures", so maybe OnUserGesture().  I don't feel strongly though.

+
   // 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
   // caller destroys the Subscription object.
   virtual scoped_ptr<PresentationConnectionStateSubscription>
   AddPresentationConnectionStateChangedCallback(
       const MediaRoute::Id& route_id,
       const content::PresentationConnectionStateChangedCallback& callback) = 0;
 
   // Called when the off the record (incognito) profile for this instance is
@@ skipping 58 matching lines @@
 
   // Unregisters a previously registered PresentationSessionMessagesObserver.
   // |observer| will stop receiving further updates.
   virtual void UnregisterPresentationSessionMessagesObserver(
       PresentationSessionMessagesObserver* observer) = 0;
 };
 
 }  // namespace media_router
 
 #endif  // CHROME_BROWSER_MEDIA_ROUTER_MEDIA_ROUTER_H_