Fix unexpected blurry text caused by combination of skew and promotion

third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp

 /*
  * Copyright (C) 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2014 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 521 matching lines @@
         isCompositedWithInlineTransform)
       currentRecursionData.m_testingOverlap = false;
 
     if (childRecursionData.m_compositingAncestor == layer)
       overlapMap.finishCurrentOverlapTestingContext();
 
     descendantHas3DTransform |=
         anyDescendantHas3DTransform || layer->has3DTransform();
   }
 
+  // Promote skewed elements within a promoted skewed element to improve
+  // output quality.
+  if (canBeComposited && ancestorLayer &&
+      ancestorLayer->getCompositingReasons()) {

[flackr, 2017/02/25 15:16:19]

Only if the ancestor was also skewed. If the ancestor layer was not skewed then
we don't need to promote skewed descendants. We might need to make this part of
CompositingRequirementsUpdater::RecursionData so that we don't have to search up
the tree every time.

[yigu, 2017/02/27 22:03:41]

Done.

+    if (layer->layoutObject().styleRef().hasTransform()) {
+      for (const auto& operation :
+           layer->layoutObject().styleRef().transform().operations()) {

[flackr, 2017/02/25 15:16:19]

Move this to TransformOperations::hasSkew.

[yigu, 2017/02/27 22:03:42]

Done.

+        TransformOperation::OperationType type = operation->type();
+        if (type == TransformOperation::Skew ||
+            type == TransformOperation::SkewX ||
+            type == TransformOperation::SkewY) {
+          reasonsToComposite |=
+              CompositingReasonLayerForTextWithinSkewedPromotedElement;
+        }
+      }
+    }
+  }
+
   // At this point we have finished collecting all reasons to composite this
   // layer.
   layer->setCompositingReasons(reasonsToComposite);
 }
 
 }  // namespace blink