[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;
 
+  // Returns |true| if mDNS discovery is enabled.
+  virtual bool should_enable_mdns_discovery() const = 0;

[mark a. foltz, 2016/03/25 23:14:16]

But the method sounds like mdns will be enabled in the future?  Consider naming
this is_mdns_enabled()

[btolsch, 2016/03/26 10:53:58]

Due to other changes, it turns out this is no longer needed so I removed it.
This also slightly cleans up the Android and test code that was forced to
"implement" these methods.

+
+  // Enables mDNS discovery on Media Route Provider Manager.
+  // |should_enable_mdns_discovery| should also return |true| after this call.
+  virtual void EnsureMdnsDiscoveryEnabled() = 0;

[mark a. foltz, 2016/03/25 23:14:16]

I don't feel great about exposing this API at the MediaRouter level.  It's
really an API to trigger a specific codepath on a specific platform (Windows) in
response to something happening in the UI.

Maybe there's a slightly more general way to think about this flow, like naming
it OnMediaSinkSelection() or OnUserInteraction(), which is implemented by
enabling mDNS if necessary.  

I don't want to derail this into a bikeshed, but consider adding a TODO() to
make this API more generic if we find other use cases that follow the same
pattern.

[btolsch, 2016/03/26 10:53:58]

I think that since should_enable_mdns_discovery() was removed it is simple to
rename this to OnUserInteraction() now.

+
   // 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_