Bug 1402824 - Include nsIThreadInteral.h in SynchronizedEventQueue to fix non-unified. r=billm

nsIThreadObserver (defined in nsIThreadInternal.h) was used without prior
declaration.

MozReview-Commit-ID: 9cSuERgUPtl

--HG--
extra : rebase_source : b7a3a47114680dbb69c9d0f17fa75ebbc8f444dc

xpcom/threads/SynchronizedEventQueue.cpp

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