Bug 1402824 - Include nsIRunnable in EventQueue.cpp to fix non-unified build. r=billm

nsIRunnable was used without prior declaration.

MozReview-Commit-ID: CVEkaw6xBsC

--HG--
extra : rebase_source : 95b377eda3befeed66f37e6833a680ae4333303c

xpcom/threads/EventQueue.cpp

@@ -5,6 +5,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "mozilla/EventQueue.h"
+#include "nsIRunnable.h"
 
 using namespace mozilla;