[CSS Blending] Implement mix-blend-mode in software.

Source/core/rendering/RenderLayer.h

Index: Source/core/rendering/RenderLayer.h
diff --git a/Source/core/rendering/RenderLayer.h b/Source/core/rendering/RenderLayer.h
index 6b944ddb48089a66743a8b96b4f128eea1a6ee38..d3c3de48eaef1a378861bd5d95d202445c981ad3 100644
--- a/Source/core/rendering/RenderLayer.h
+++ b/Source/core/rendering/RenderLayer.h
@@ -825,6 +825,8 @@ private:
 
     bool isDirtyStackingContainer() const { return m_zOrderListsDirty && isStackingContainer(); }
 
+    bool hasNonAcceleratedBlendedChildInCurrentStackingContext() const;
+
     void setAncestorChainHasSelfPaintingLayerDescendant();
     void dirtyAncestorChainHasSelfPaintingLayerDescendantStatus();
 
@@ -1137,6 +1139,9 @@ protected:
     unsigned m_usedTransparency : 1; // Tracks whether we need to close a transparent layer, i.e., whether
                                  // we ended up painting this layer or any descendants (and therefore need to
                                  // blend).
+    unsigned m_isolateLayerFromBlendedContent : 1; // Blending through the mix-blend-mode operation should
+        // only be performed with the contents of the underlying
+        // stacking context.
     unsigned m_paintingInsideReflection : 1; // A state bit tracking if we are painting inside a replica.
     unsigned m_inOverflowRelayout : 1;
     unsigned m_repaintStatus : 2; // RepaintStatus