Use static XPF for porter duff xp factories.

src/gpu/effects/GrPorterDuffXferProcessor.h

Index: src/gpu/effects/GrPorterDuffXferProcessor.h
diff --git a/src/gpu/effects/GrPorterDuffXferProcessor.h b/src/gpu/effects/GrPorterDuffXferProcessor.h
index 474285d829ea69c9dadc970a3d9dcfe474106c87..d210a81755a3296580772e1733ce5f26956fb9ee 100644
--- a/src/gpu/effects/GrPorterDuffXferProcessor.h
+++ b/src/gpu/effects/GrPorterDuffXferProcessor.h
@@ -53,6 +53,8 @@ private:
 
 class GrPorterDuffXPFactory : public GrXPFactory {
 public:
+    static GrXPFactory* Create(SkXfermode::Mode mode); 
+
     static GrXPFactory* Create(SkXfermode::Coeff src, SkXfermode::Coeff dst) {
         return SkNEW_ARGS(GrPorterDuffXPFactory, ((GrBlendCoeff)(src), (GrBlendCoeff)(dst)));
     }