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 aada21668d2aeabe3d149fa3e8ad5fe5988748ad..b34b665d9573866bc5704a40751035ede7e80f3b 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() == EMaskSourceType::MaskLuminance);
             context->drawTiledImage(image.get(), geometry.destRect(), geometry.relativePhase(), geometry.tileSize(),
                 compositeOp, useLowQualityScaling, bgLayer->blendMode());
         }