[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 eda86ab0ad3b781cb042bff10d80cb8f2562ef1a..4907c9b92e9c45f51f376da67b09b8c6fda865af 100644
--- a/Source/core/rendering/RenderLayer.h
+++ b/Source/core/rendering/RenderLayer.h
@@ -829,6 +829,8 @@ private:
 
     bool isDirtyStackingContainer() const { return m_zOrderListsDirty && isStackingContainer(); }
 
+    bool hasNonAcceleratedBlendedChildInCurrentStackingContext() const;
+
     void setAncestorChainHasSelfPaintingLayerDescendant();
     void dirtyAncestorChainHasSelfPaintingLayerDescendantStatus();
 
@@ -1147,6 +1149,9 @@ 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

[shawnsingh, 2013/09/19 11:05:56]

Some nitpicks here - 

(1) Is it correct to say "A layer with a mix-blend-mode should only be blended
with content underneath this layer, within the same stacking context" ?  I think
that would be more clear.   The word "underlying" here (and actually, also in
the spec) feels a bit unclear to me.

(2) In my opinion, the name "m_isolateForDescendantBlendMode" might be clearer
here. 

[mitica, 2013/09/19 11:49:00]

Sounds good, I'll change it.

+        // 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