[SPv2] Add CSS mask support

third_party/WebKit/Source/core/paint/PaintLayer.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@web.de>
@@ skipping 2656 matching lines @@
   }
   if (m_rareData || groupedMapping)
     ensureRareData().groupedMapping = groupedMapping;
 #if DCHECK_IS_ON()
   DCHECK(!groupedMapping || groupedMapping->verifyLayerInSquashingVector(this));
 #endif
   if (options == InvalidateLayerAndRemoveFromMapping && groupedMapping)
     groupedMapping->setNeedsGraphicsLayerUpdate(GraphicsLayerUpdateSubtree);
 }
 
 bool PaintLayer::hasCompositedMask() const {

[trchen, 2017/01/21 01:27:08]

Is it obvious to you why this change is needed? I feel this function could use
some good comments.

[chrishtr, 2017/01/24 01:16:28]

Maybe just rename the method to something like
applyBlendToMaskOutputWhenPainting?
It's pretty obvious what the two callsites are doing to anyone who needs to
know.

[trchen, 2017/02/11 02:35:45]

"maskBlendingAppliedByCompositor" to avoid negation. Also code reads better in
my totally subject opinion. :D

+  DCHECK(m_layoutObject->hasMask());
+  if (RuntimeEnabledFeatures::slimmingPaintV2Enabled())
+    return true;
   return m_rareData && m_rareData->compositedLayerMapping &&
          m_rareData->compositedLayerMapping->hasMaskLayer();
 }
 
 bool PaintLayer::hasCompositedClippingMask() const {
   return m_rareData && m_rareData->compositedLayerMapping &&
          m_rareData->compositedLayerMapping->hasChildClippingMaskLayer();
 }
 
 bool PaintLayer::paintsWithTransform(GlobalPaintFlags globalPaintFlags) const {
@@ skipping 533 matching lines @@
 }
 
 void showLayerTree(const blink::LayoutObject* layoutObject) {
   if (!layoutObject) {
     LOG(INFO) << "Cannot showLayerTree. Root is (nil)";
     return;
   }
   showLayerTree(layoutObject->enclosingLayer());
 }
 #endif