Add missing clone method to GrMorphologyEffect

Change-Id: Id0e435e7f8d055db336e5be80ae1c308197dd950
Reviewed-on: https://skia-review.googlesource.com/28042
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/src/effects/SkMorphologyImageFilter.cpp b/src/effects/SkMorphologyImageFilter.cpp
index c0ac576..19481ac 100644
--- a/src/effects/SkMorphologyImageFilter.cpp
+++ b/src/effects/SkMorphologyImageFilter.cpp
@@ -163,6 +163,10 @@
 
     const char* name() const override { return "Morphology"; }
 
+    sk_sp<GrFragmentProcessor> clone() const override {
+        return sk_sp<GrFragmentProcessor>(new GrMorphologyEffect(*this));
+    }
+
 private:
     GrCoordTransform fCoordTransform;
     TextureSampler fTextureSampler;