Bug 1571081 - Make MediaKeys correctly specify a NS_INTERFACE_MAP_ENTRY for nsISupports. r=mccr8

Bug 1522547 overlooked the need for specifying map entries for both nsISupports
and nsIDocumentActivity and only had the latter. This changeset adds the missing
nsISupports case.

Differential Revision: https://phabricator.services.mozilla.com/D42563

--HG--
extra : moz-landing-system : lando

dom/media/eme/MediaKeys.cpp

@@ -65,6 +65,7 @@ NS_IMPL_CYCLE_COLLECTING_ADDREF(MediaKeys)
 NS_IMPL_CYCLE_COLLECTING_RELEASE(MediaKeys)
 NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(MediaKeys)
   NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
   NS_INTERFACE_MAP_ENTRY(nsIDocumentActivity)
 NS_INTERFACE_MAP_END