Use SkXfermode as public facing enum for GrPorterDuffXP

src/effects/SkBlurMaskFilter.cpp

Index: src/effects/SkBlurMaskFilter.cpp
diff --git a/src/effects/SkBlurMaskFilter.cpp b/src/effects/SkBlurMaskFilter.cpp
index b521546a8004558542a7ca871d7a96cc16b13f53..bce46ec85a34b7fd2d53464069f46c5144b4edfc 100644
--- a/src/effects/SkBlurMaskFilter.cpp
+++ b/src/effects/SkBlurMaskFilter.cpp
@@ -1220,15 +1220,15 @@ bool SkBlurMaskFilterImpl::filterMaskGPU(GrTexture* src,
         paint.addColorProcessor(GrSimpleTextureEffect::Create(src, matrix))->unref();
         if (kInner_SkBlurStyle == fBlurStyle) {
             // inner:  dst = dst * src
-            paint.setPorterDuffXPFactory(kDC_GrBlendCoeff, kZero_GrBlendCoeff);
+            paint.setPorterDuffXPFactory(SkXfermode::kDC_Coeff, SkXfermode::kZero_Coeff);
         } else if (kSolid_SkBlurStyle == fBlurStyle) {
             // solid:  dst = src + dst - src * dst
             //             = (1 - dst) * src + 1 * dst
-            paint.setPorterDuffXPFactory(kIDC_GrBlendCoeff, kOne_GrBlendCoeff);
+            paint.setPorterDuffXPFactory(SkXfermode::kIDC_Coeff, SkXfermode::kOne_Coeff);
         } else if (kOuter_SkBlurStyle == fBlurStyle) {
             // outer:  dst = dst * (1 - src)
             //             = 0 * src + (1 - src) * dst
-            paint.setPorterDuffXPFactory(kZero_GrBlendCoeff, kISC_GrBlendCoeff);
+            paint.setPorterDuffXPFactory(SkXfermode::kZero_Coeff, SkXfermode::kISC_Coeff);
         }
         context->drawRect(paint, SkMatrix::I(), clipRect);
     }