[Media Router] Wire through a new MRPM call to update media sinks.

chrome/browser/media/router/mojo/media_router.mojom

Index: chrome/browser/media/router/mojo/media_router.mojom
diff --git a/chrome/browser/media/router/mojo/media_router.mojom b/chrome/browser/media/router/mojo/media_router.mojom
index 683904122489d906d2ffbca2765f76648c824c13..07b918dc744fac7f764d199971b1fc3f4a936436 100644
--- a/chrome/browser/media/router/mojo/media_router.mojom
+++ b/chrome/browser/media/router/mojo/media_router.mojom
@@ -286,6 +286,10 @@ interface MediaRouteProvider {
   // Calling this will trigger a firewall prompt on Windows if there is not
   // already a firewall rule for mDNS.
   EnableMdnsDiscovery();
+
+  // Starts discovery. No-op for MRPs which have already registered discovery
+  // listeners.
+  StartDiscovery();
 };
 
 // Interface for a service which observes state changes across media