Skip PaintPhaseDescendantBlockBackgroundsOnly phase if possible

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 dd5f4f5142708bd1199a8da0aaab94d59007832c..6d9cb1d13a5cc7cb00acfc70d3055bd282651974 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.h
@@ -672,6 +672,9 @@ public:
     bool needsPaintPhaseFloat() const { return m_needsPaintPhaseFloat; }
     void setNeedsPaintPhaseFloat() { ASSERT(isSelfPaintingLayer()); m_needsPaintPhaseFloat = true; }
 
+    bool needsPaintPhaseDescendantBlockBackgrounds() const { return m_needsPaintPhaseDescendantBlockBackgrounds; }
+    void setNeedsPaintPhaseDescendantBlockBackgrounds() { ASSERT(isSelfPaintingLayer()); m_needsPaintPhaseDescendantBlockBackgrounds = true; }
+
     PaintTiming* paintTiming();
 
 private:
@@ -813,6 +816,7 @@ private:
 
     unsigned m_needsPaintPhaseDescendantOutlines : 1;
     unsigned m_needsPaintPhaseFloat : 1;
+    unsigned m_needsPaintPhaseDescendantBlockBackgrounds : 1;
 
     // These bitfields are part of ancestor/descendant dependent compositing inputs.
     unsigned m_hasDescendantWithClipPath : 1;