Bug 518924. Fix memory leak in NPAPI async callback test and re-enable

modules/plugin/test/mochitest/Makefile.in

@@ -70,10 +70,10 @@ _MOCHITEST_FILES = \
 		test_streamNotify.html \
 		test_instantiation.html \
 		test_cookies.html \
+		test_npn_timers.html \
+		test_npn_asynccall.html \
 		$(NULL)
 
-#		test_npn_timers.html \ disabled for leaking
-#		test_npn_asynccall.html \ disabled for leaking
 #		test_npruntime_npnsetexception.html \ Disabled for e10s
 
 ifdef MOZ_IPC

modules/plugin/test/testplugin/nptest.cpp

@@ -2425,6 +2425,7 @@ asyncCallback(void* cookie)
       BOOLEAN_TO_NPVARIANT(id->asyncCallbackResult, arg);
       NPN_Invoke(npp, windowObject, NPN_GetStringIdentifier(id->asyncTestScriptCallback.c_str()), &arg, 1, &rval);
       NPN_ReleaseVariantValue(&arg);
+      NPN_ReleaseObject(windowObject);
       break;
   }
 }