Bug 1199643 - Fix unsafe use of PerformanceGroup. r=jandem

--HG--
extra : transplant_source : %C6%29Z%EE%CE%01%9B%D6%E6%07%20%ADl1%A8%D8%C6%9E%05%06

js/src/jsapi.cpp

@@ -333,7 +333,7 @@ IterPerformanceStats(JSContext* cx,
             continue;
         }
         js::AutoCompartment autoCompartment(cx, compartment);
-        PerformanceGroup* group = compartment->performanceMonitoring.getSharedGroup(cx);
+        mozilla::RefPtr<PerformanceGroup> group = compartment->performanceMonitoring.getSharedGroup(cx);
         if (group->data.ticks == 0) {
             // Don't report compartments that have never been used.
             continue;