Fix CSS clips cannot be correctly handled by composited scroller

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 1736 matching lines @@
       !layer->compositor()->preferCompositingToLCDTextEnabled() &&
       !backgroundSupportsLCDText)
     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());
+           layer->layoutObject()->style()->hasBorderRadius() ||
+           !layer->layoutObject()->style()->hasAutoClip());

[chrishtr, 2016/12/28 16:17:44]

Instead, write this:

layer->layoutObject()->hasClip()

[yigu, 2016/12/28 18:42:06]

Done.

 }
 
 void PaintLayerScrollableArea::updateNeedsCompositedScrolling(
     LCDTextMode mode) {
   const bool needsCompositedScrolling =
       layerNeedsCompositedScrolling(mode, layer());
   if (static_cast<bool>(m_needsCompositedScrolling) !=
       needsCompositedScrolling) {
     m_needsCompositedScrolling = needsCompositedScrolling;
     layer()->didUpdateNeedsCompositedScrolling();
@@ skipping 258 matching lines @@
 
 void PaintLayerScrollableArea::DelayScrollOffsetClampScope::
     clampScrollableAreas() {
   for (auto& scrollableArea : *s_needsClamp)
     scrollableArea->clampScrollOffsetAfterOverflowChange();
   delete s_needsClamp;
   s_needsClamp = nullptr;
 }
 
 }  // namespace blink