Implement SVG masking with slimming paint

public/platform/WebDisplayItemList.h

Index: public/platform/WebDisplayItemList.h
diff --git a/public/platform/WebDisplayItemList.h b/public/platform/WebDisplayItemList.h
index c2281cd7591cfb17678718fb30b30c0b4ba47659..7cb5c40e85cd133c4d0a2885677a02050397ecc3 100644
--- a/public/platform/WebDisplayItemList.h
+++ b/public/platform/WebDisplayItemList.h
@@ -12,8 +12,10 @@
 #include "WebSize.h"
 #include "WebVector.h"
 
+#include "third_party/skia/include/core/SkColorFilter.h"
 #include "third_party/skia/include/core/SkRRect.h"
 #include "third_party/skia/include/core/SkRegion.h"
+#include "third_party/skia/include/core/SkXfermode.h"
 #include "third_party/skia/include/utils/SkMatrix44.h"
 
 // FIXME: Remove this once references to this macro in chromium are removed.
@@ -47,6 +49,9 @@ public:
     virtual void appendEndTransformItem() = 0;
     virtual void appendTransparencyItem(float opacity, WebBlendMode) = 0;
     virtual void appendEndTransparencyItem() = 0;
+    virtual void appendCompositingItem(float opacity,
+        SkXfermode::Mode, SkColorFilter*) = 0;
+    virtual void appendEndCompositingItem() = 0;
 
     virtual void appendFilterItem(const WebFilterOperations&, const WebFloatRect& bounds) = 0;
     virtual void appendEndFilterItem() = 0;