Implement CSS luminance masking using skia SkLumaMaskXfermode class.

Source/core/rendering/RenderBoxModelObject.cpp

Index: Source/core/rendering/RenderBoxModelObject.cpp
diff --git a/Source/core/rendering/RenderBoxModelObject.cpp b/Source/core/rendering/RenderBoxModelObject.cpp
index 415f526aea75777c0fc7930c0fc4b7b8af54f060..932db84e2a01905a1926066b8f1bb04e49f1d64a 100644
--- a/Source/core/rendering/RenderBoxModelObject.cpp
+++ b/Source/core/rendering/RenderBoxModelObject.cpp
@@ -742,6 +742,7 @@ void RenderBoxModelObject::paintFillLayerExtended(const PaintInfo& paintInfo, co
             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() == MaskLuminance);
             context->drawTiledImage(image.get(), geometry.destRect(), geometry.relativePhase(), geometry.tileSize(),
                 compositeOp, useLowQualityScaling, bgLayer->blendMode());
         }