Fix unexpected blurry text caused by combination of skew and promotion

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

Index: third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
index aca28342b55b0d8d63095c2406bf06611a14e85a..b379b908560023c15087ccd1485e6e002dc0f1b8 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositingRequirementsUpdater.cpp
@@ -147,13 +147,15 @@ class CompositingRequirementsUpdater::RecursionData {
         m_subtreeIsCompositing(false),
         m_hasUnisolatedCompositedBlendingDescendant(false),
         m_testingOverlap(true),
-        m_hasCompositedScrollingAncestor(false) {}
+        m_hasCompositedScrollingAncestor(false),
+        m_hasCompositedSkewedAncestor(false) {}
 
   PaintLayer* m_compositingAncestor;
   bool m_subtreeIsCompositing;
   bool m_hasUnisolatedCompositedBlendingDescendant;
   bool m_testingOverlap;
   bool m_hasCompositedScrollingAncestor;
+  bool m_hasCompositedSkewedAncestor;
 };
 
 static bool requiresCompositingOrSquashing(CompositingReasons reasons) {
@@ -517,6 +519,36 @@ void CompositingRequirementsUpdater::updateRecursive(
     if (willBeCompositedOrSquashed)
       currentRecursionData.m_subtreeIsCompositing = true;
 
+    // If an skewed element is composited due to its descendants, we have to

[flackr, 2017/02/28 21:40:14]

We want the opposite behavior, the descendant should be composited if its
ancestor is skewed and was composited.

+    // update the uncomposited skewed descendants to composite them.
+    if (currentRecursionData.m_subtreeIsCompositing &&
+        layer->layoutObject().styleRef().hasTransform() &&
+        layer->layoutObject().styleRef().transform().hasSkew()) {
+      childRecursionData.m_hasCompositedSkewedAncestor = true;
+
+      PaintLayerStackingNodeIterator iterator(
+          *layer->stackingNode(), NormalFlowChildren | PositiveZOrderChildren);
+      while (PaintLayerStackingNode* curNode = iterator.next()) {
+        IntRect absoluteChildDescendantBoundingBox;
+        updateRecursive(layer, curNode->layer(), overlapMap, childRecursionData,
+                        anyDescendantHas3DTransform, unclippedDescendants,
+                        absoluteChildDescendantBoundingBox);
+        absoluteDescendantBoundingBox.unite(absoluteChildDescendantBoundingBox);
+      }
+    }
+
+    // Promote skewed elements within a promoted skewed element to improve
+    // output quality.
+    if (canBeComposited && !willBeCompositedOrSquashed &&
+        currentRecursionData.m_hasCompositedSkewedAncestor) {
+      if (layer->layoutObject().styleRef().hasTransform()) {
+        if (layer->layoutObject().styleRef().transform().hasSkew()) {
+          reasonsToComposite |=
+              CompositingReasonSkewWithCompositedSkewedAncestor;
+        }
+      }
+    }
+
     // Turn overlap testing off for later layers if it's already off, or if we
     // have an animating transform.  Note that if the layer clips its
     // descendants, there's no reason to propagate the child animation to the