Bug 1216851 - Don't include event regions when deciding if we can flatten opacity. r=roc

--HG--
extra : rebase_source : 5bc16d6c15e5063b565dccafef71bf3a83744009

layout/base/nsDisplayList.cpp

@@ -3962,6 +3962,10 @@ nsDisplayOpacity::ShouldFlattenAway(nsDisplayListBuilder* aBuilder)
   bool snap;
   uint32_t numChildren = 0;
   for (; numChildren < ArrayLength(children) && child; numChildren++, child = child->GetAbove()) {
+    if (child->GetType() == nsDisplayItem::TYPE_LAYER_EVENT_REGIONS) {
+      numChildren--;
+      continue;
+    }
     if (!child->CanApplyOpacity()) {
       return false;
     }