[SPv2] Add CSS mask support

third_party/WebKit/Source/core/paint/BoxPainter.cpp

Index: third_party/WebKit/Source/core/paint/BoxPainter.cpp
diff --git a/third_party/WebKit/Source/core/paint/BoxPainter.cpp b/third_party/WebKit/Source/core/paint/BoxPainter.cpp
index a4ca99e2cc0665f07b38d81b235a74afa2ef81f8..bb81359501802a34989f70d11dbc354555e94a4c 100644
--- a/third_party/WebKit/Source/core/paint/BoxPainter.cpp
+++ b/third_party/WebKit/Source/core/paint/BoxPainter.cpp
@@ -816,14 +816,15 @@ void BoxPainter::paintMaskImages(const PaintInfo& paintInfo,
                                  const LayoutRect& paintRect) {
   // Figure out if we need to push a transparency layer to render our mask.
   bool pushTransparencyLayer = false;
-  bool compositedMask =
-      m_layoutBox.hasLayer() && m_layoutBox.layer()->hasCompositedMask();
   bool flattenCompositingLayers =
       paintInfo.getGlobalPaintFlags() & GlobalPaintFlattenCompositingLayers;
+  bool maskBlendingAppliedByCompositor =
+      !flattenCompositingLayers && m_layoutBox.hasLayer() &&
+      m_layoutBox.layer()->maskBlendingAppliedByCompositor();
 
   bool allMaskImagesLoaded = true;
 
-  if (!compositedMask || flattenCompositingLayers) {
+  if (!maskBlendingAppliedByCompositor) {
     pushTransparencyLayer = true;
     StyleImage* maskBoxImage = m_layoutBox.style()->maskBoxImage().image();
     const FillLayer& maskLayers = m_layoutBox.style()->maskLayers();