Don't create a GXPFactory when blend is SrcOver

src/effects/SkMorphologyImageFilter.cpp

Index: src/effects/SkMorphologyImageFilter.cpp
diff --git a/src/effects/SkMorphologyImageFilter.cpp b/src/effects/SkMorphologyImageFilter.cpp
index fbc071fe5887b7f8464df407895ce560ef9c4bc7..484ed57f37bc8904d36670cb490dd6f8c1086f8c 100644
--- a/src/effects/SkMorphologyImageFilter.cpp
+++ b/src/effects/SkMorphologyImageFilter.cpp
@@ -479,6 +479,7 @@ void apply_morphology_rect(GrDrawContext* drawContext,
                                                                radius,
                                                                morphType,
                                                                bounds))->unref();
+    paint.setPorterDuffXPFactory(SkXfermode::kSrc_Mode);
     drawContext->fillRectToRect(clip, paint, SkMatrix::I(), SkRect::Make(dstRect),
                                      SkRect::Make(srcRect));
 }
@@ -496,6 +497,7 @@ void apply_morphology_rect_no_bounds(GrDrawContext* drawContext,
                                                                direction,
                                                                radius,
                                                                morphType))->unref();
+    paint.setPorterDuffXPFactory(SkXfermode::kSrc_Mode);
     drawContext->fillRectToRect(clip, paint, SkMatrix::I(), SkRect::Make(dstRect),
                                 SkRect::Make(srcRect));
 }