Update PaintLayer::needsPaintPhaseXXX flags when add/remove layer on style change

third_party/WebKit/Source/core/paint/PaintLayer.h

Index: third_party/WebKit/Source/core/paint/PaintLayer.h
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.h b/third_party/WebKit/Source/core/paint/PaintLayer.h
index 4749c706032e32bc76e0331be327bd09f87e4ff1..44e4ec1427571fd6be7f56c0182aa8e7e96d3e57 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.h
@@ -229,8 +229,8 @@ public:
     void addChild(PaintLayer* newChild, PaintLayer* beforeChild = 0);
     PaintLayer* removeChild(PaintLayer*);
 
-    void removeOnlyThisLayer();
-    void insertOnlyThisLayer();
+    void removeOnlyThisLayerAfterStyleChange();
+    void insertOnlyThisLayerAfterStyleChange();
 
     void styleChanged(StyleDifference, const ComputedStyle* oldStyle);
 
@@ -670,6 +670,7 @@ public:
 
     // Used to skip PaintPhaseDescendantOutlinesOnly for layers that have never had descendant outlines.
     // Once it's set we never clear it because it's not easy to track if all outlines have been removed.
+    // For more details, see core/paint/REAME.md#Empty paint phase optimization.
     bool needsPaintPhaseDescendantOutlines() const { return m_needsPaintPhaseDescendantOutlines; }
     void setNeedsPaintPhaseDescendantOutlines() { ASSERT(isSelfPaintingLayer()); m_needsPaintPhaseDescendantOutlines = true; }
 
@@ -772,6 +773,13 @@ private:
         return *m_rareData;
     }
 
+    void mergeNeedsPaintPhaseFlagsFrom(const PaintLayer& layer)
+    {
+        m_needsPaintPhaseDescendantOutlines |= layer.m_needsPaintPhaseDescendantOutlines;
+        m_needsPaintPhaseFloat |= layer.m_needsPaintPhaseFloat;
+        m_needsPaintPhaseDescendantBlockBackgrounds |= layer.m_needsPaintPhaseDescendantBlockBackgrounds;
+    }
+
     unsigned m_layerType : 2; // PaintLayerType
 
     // Self-painting layer is an optimization where we avoid the heavy Layer painting