Bug 1107143 - Don't build event regions unless we're painting to the window. r=tnikkel

MozReview-Commit-ID: LRN8S7buXLL

--HG--
extra : rebase_source : 608e7f32c272f0154a509cab31be34c98ade5845

layout/base/nsDisplayList.cpp

@@ -1420,7 +1420,7 @@ nsDisplayListBuilder::GetDirtyRectForScrolledContents(const nsIFrame* aScrollabl
 bool
 nsDisplayListBuilder::IsBuildingLayerEventRegions()
 {
-  if (mMode == PAINTING) {
+  if (IsPaintingToWindow()) {
     // Note: this function and LayerEventRegionsEnabled are the only places
     // that get to query LayoutEventRegionsEnabled 'directly' - other code
     // should call this function.