Implement CSS luminance masking using skia SkLumaMaskXfermode class.

Source/core/rendering/RenderBoxModelObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 724 matching lines @@
     // no progressive loading of the background image
     if (shouldPaintBackgroundImage) {
         BackgroundImageGeometry geometry;
         calculateBackgroundImageGeometry(bgLayer, scrolledPaintRect, geometry, backgroundObject);
         geometry.clip(paintInfo.rect);
         if (!geometry.destRect().isEmpty()) {
             CompositeOperator compositeOp = op == CompositeSourceOver ? bgLayer->composite() : op;
             RenderObject* clientForBackgroundImage = backgroundObject ? backgroundObject : this;
             RefPtr<Image> image = bgImage->image(clientForBackgroundImage, geometry.tileSize());
             bool useLowQualityScaling = shouldPaintAtLowQuality(context, image.get(), bgLayer, geometry.tileSize());
+            context->setDrawLuminanceMask(bgLayer->maskSourceType() == EMaskSourceType::MaskLuminance);
             context->drawTiledImage(image.get(), geometry.destRect(), geometry.relativePhase(), geometry.tileSize(),
                 compositeOp, useLowQualityScaling, bgLayer->blendMode());
         }
     }
 
     if (bgLayer->clip() == TextFillBox) {
         // Create the text mask layer.
         context->setCompositeOperation(CompositeDestinationIn);
         context->beginTransparencyLayer(1);
 
@@ skipping 2031 matching lines @@
     ASSERT(!beforeChild || toBoxModelObject == beforeChild->parent());
     for (RenderObject* child = startChild; child && child != endChild; ) {
         // Save our next sibling as moveChildTo will clear it.
         RenderObject* nextSibling = child->nextSibling();
         moveChildTo(toBoxModelObject, child, beforeChild, fullRemoveInsert);
         child = nextSibling;
     }
 }
 
 } // namespace WebCore