Bug 1286709 - Assert the non-nullness of an GetApzc() call's return value. r=kats.

--HG--
extra : rebase_source : 28310216275e7f919314e92559ea79cb0692b69e

gfx/layers/composite/AsyncCompositionManager.cpp

@@ -1106,6 +1106,7 @@ ApplyAsyncTransformToScrollbarForContent(Layer* aScrollbar,
 
   const FrameMetrics& metrics = aContent.Metrics();
   AsyncPanZoomController* apzc = aContent.GetApzc();
+  MOZ_RELEASE_ASSERT(apzc);
 
   AsyncTransformComponentMatrix asyncTransform =
     apzc->GetCurrentAsyncTransform(AsyncPanZoomController::RESPECT_FORCE_DISABLE);