Bug 1107353 - Wallpaper a null-pointer crash in AsyncScrollCallback for now. r=kip

layout/generic/nsGfxScrollFrame.cpp

@@ -1965,10 +1965,14 @@ void
 ScrollFrameHelper::AsyncScrollCallback(ScrollFrameHelper* aInstance,
                                        mozilla::TimeStamp aTime)
 {
-  NS_ASSERTION(aInstance != nullptr, "aInstance must not be null");
-  NS_ASSERTION(aInstance->mAsyncScroll,
+  MOZ_ASSERT(aInstance != nullptr, "aInstance must not be null");
+  MOZ_ASSERT(aInstance->mAsyncScroll,
     "Did not expect AsyncScrollCallback without an active async scroll.");
 
+  if (!aInstance || !aInstance->mAsyncScroll) {
+    return;  // XXX wallpaper bug 1107353 for now.
+  }
+
   nsRect range = aInstance->mAsyncScroll->mRange;
   if (aInstance->mAsyncScroll->mIsSmoothScroll) {
     if (!aInstance->mAsyncScroll->IsFinished(aTime)) {