Add transform and background not opaque as main thread scrolling reasons

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights
  * reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@gmail.com>
@@ skipping 1735 matching lines @@
           toLayoutBox(layer->layoutObject())->paddingBoxRect()) &&
       !layer->compositesWithTransform() && !layer->compositesWithOpacity();
 
   if (mode == PaintLayerScrollableArea::ConsiderLCDText &&
       !layer->compositor()->preferCompositingToLCDTextEnabled() &&
       !backgroundSupportsLCDText) {
     if (layer->compositesWithOpacity()) {
       addStyleRelatedMainThreadScrollingReasons(
           MainThreadScrollingReason::kHasOpacity);
     }
+    if (layer->compositesWithTransform()) {
+      addStyleRelatedMainThreadScrollingReasons(
+          MainThreadScrollingReason::kHasTransform);
+    }
+    if (!layer->backgroundIsKnownToBeOpaqueInRect(
+            toLayoutBox(layer->layoutObject())->paddingBoxRect())) {
+      addStyleRelatedMainThreadScrollingReasons(
+          MainThreadScrollingReason::kBackgroundNotOpaqueInRect);
+    }
     return false;
   }
 
   // TODO(schenney) Tests fail if we do not also exclude
   // layer->layoutObject()->style()->hasBorderDecoration() (missing background
   // behind dashed borders). Resolve this case, or not, and update this check
   // with the results.
   return !(layer->size().isEmpty() || layer->hasDescendantWithClipPath() ||
            layer->hasAncestorWithClipPath() ||
            layer->layoutObject()->style()->hasBorderRadius() ||
@@ skipping 306 matching lines @@
 
 void PaintLayerScrollableArea::DelayScrollOffsetClampScope::
     clampScrollableAreas() {
   for (auto& scrollableArea : *s_needsClamp)
     scrollableArea->clampScrollOffsetAfterOverflowChange();
   delete s_needsClamp;
   s_needsClamp = nullptr;
 }
 
 }  // namespace blink