change flattenable factory to return sk_sp

src/effects/SkAlphaThresholdFilter.cpp

Index: src/effects/SkAlphaThresholdFilter.cpp
diff --git a/src/effects/SkAlphaThresholdFilter.cpp b/src/effects/SkAlphaThresholdFilter.cpp
index 1c79c45194477f278c62e16282c69559d8aaf4e8..5a9ad79a9ddef9ee5b1535541c8e08481e1ff1a9 100644
--- a/src/effects/SkAlphaThresholdFilter.cpp
+++ b/src/effects/SkAlphaThresholdFilter.cpp
@@ -265,13 +265,13 @@ void AlphaThresholdEffect::onComputeInvariantOutput(GrInvariantOutput* inout) co
 
 #endif
 
-SkFlattenable* SkAlphaThresholdFilterImpl::CreateProc(SkReadBuffer& buffer) {
+sk_sp<SkFlattenable> SkAlphaThresholdFilterImpl::CreateProc(SkReadBuffer& buffer) {
     SK_IMAGEFILTER_UNFLATTEN_COMMON(common, 1);
     SkScalar inner = buffer.readScalar();
     SkScalar outer = buffer.readScalar();
     SkRegion rgn;
     buffer.readRegion(&rgn);
-    return SkAlphaThresholdFilter::Make(rgn, inner, outer, common.getInput(0)).release();
+    return SkAlphaThresholdFilter::Make(rgn, inner, outer, common.getInput(0));
 }
 
 SkAlphaThresholdFilterImpl::SkAlphaThresholdFilterImpl(const SkRegion& region,