Pass origin to StartObservingMediaSinks.

chrome/browser/media/router/media_router.mojom

Index: chrome/browser/media/router/media_router.mojom
diff --git a/chrome/browser/media/router/media_router.mojom b/chrome/browser/media/router/media_router.mojom
index af4b90cece83dcaeba4a206de288a2f1a6375d9c..655fc689ee58ec2dac3c8ccfbb0dc7463fee593c 100644
--- a/chrome/browser/media/router/media_router.mojom
+++ b/chrome/browser/media/router/media_router.mojom
@@ -175,7 +175,9 @@ interface MediaRouteProvider {
       => (bool sent);
 
   // Starts querying for sinks capable of displaying |media_source|.
-  StartObservingMediaSinks(string media_source);
+  // |origin| can be used to validate the media sink query to prevent

[mark a. foltz, 2016/02/17 21:50:51]

Maybe just say "to optionally verify that the origin is authorized to issue the
query."

[matt.boetger, 2016/02/18 00:50:33]

Done.

+  // fingerprinting by nefarious origins.
+  StartObservingMediaSinks(string media_source, string origin);
 
   // Stops querying sinks for |media_source|.
   StopObservingMediaSinks(string media_source);