change flattenable factory to return sk_sp

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1855733002

Review URL: https://codereview.chromium.org/1855733002
diff --git a/src/core/SkColorMatrixFilterRowMajor255.cpp b/src/core/SkColorMatrixFilterRowMajor255.cpp
index bd9a66a..c158a79 100644
--- a/src/core/SkColorMatrixFilterRowMajor255.cpp
+++ b/src/core/SkColorMatrixFilterRowMajor255.cpp
@@ -157,10 +157,10 @@
     buffer.writeScalarArray(fMatrix, 20);
 }
 
-SkFlattenable* SkColorMatrixFilterRowMajor255::CreateProc(SkReadBuffer& buffer) {
+sk_sp<SkFlattenable> SkColorMatrixFilterRowMajor255::CreateProc(SkReadBuffer& buffer) {
     SkScalar matrix[20];
     if (buffer.readScalarArray(matrix, 20)) {
-        return new SkColorMatrixFilterRowMajor255(matrix);
+        return sk_make_sp<SkColorMatrixFilterRowMajor255>(matrix);
     }
     return nullptr;
 }