Clip related property and border radius are now recorded for UMA

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 1710 matching lines @@
       return true;
   }
   return ScrollableArea::shouldScrollOnMainThread();
 }
 
 bool PaintLayerScrollableArea::computeNeedsCompositedScrolling(
     const LCDTextMode mode,
     const PaintLayer* layer) {
   if (!layer->scrollsOverflow())
     return false;
+  if (layer->size().isEmpty())

[bokan, 2017/01/05 14:52:41]

It might change behavior to have this above the `if` block below. Unless you
know it's better here, I'd leave it between the below `if` and `bool
needsCompositedScrolling`

[yigu, 2017/01/05 20:20:27]

Done.

+    return false;
 
   Node* node = layer->enclosingNode();
   if (node && node->isElementNode() &&
       (toElement(node)->compositorMutableProperties() &
        (CompositorMutableProperty::kScrollTop |
         CompositorMutableProperty::kScrollLeft)))
     return true;
 
+  bool needsCompositedScrolling = true;
+
   // TODO(flackr): Allow integer transforms as long as all of the ancestor
   // transforms are also integer.
   bool backgroundSupportsLCDText =
       RuntimeEnabledFeatures::compositeOpaqueScrollersEnabled() &&
       layer->layoutObject()->style()->isStackingContext() &&
       layer->backgroundPaintLocation() & BackgroundPaintInScrollingContents &&
       layer->backgroundIsKnownToBeOpaqueInRect(
           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;
+    needsCompositedScrolling = 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() ||
-           layer->layoutObject()->hasClip());
+  if (layer->layoutObject()->style()->hasBorderRadius()) {
+    addStyleRelatedMainThreadScrollingReasons(
+        MainThreadScrollingReason::kHasBorderRadius);
+    needsCompositedScrolling = false;
+  }
+  if (layer->layoutObject()->hasClip() ||
+      layer->layoutObject()->hasClipPath() ||
+      layer->hasDescendantWithClipPath() || layer->hasAncestorWithClipPath()) {
+    addStyleRelatedMainThreadScrollingReasons(
+        MainThreadScrollingReason::kHasClipRelatedProperty);
+    needsCompositedScrolling = false;
+  }
+  return needsCompositedScrolling;
 }
 
 void PaintLayerScrollableArea::addStyleRelatedMainThreadScrollingReasons(
     const uint32_t reason) {
   LocalFrame* frame = box().frame();
   if (!frame)
     return;
   FrameView* frameView = frame->view();
   if (!frameView)
     return;
@@ skipping 295 matching lines @@
 
 void PaintLayerScrollableArea::DelayScrollOffsetClampScope::
     clampScrollableAreas() {
   for (auto& scrollableArea : *s_needsClamp)
     scrollableArea->clampScrollOffsetAfterOverflowChange();
   delete s_needsClamp;
   s_needsClamp = nullptr;
 }
 
 }  // namespace blink