Convert SkAutoTUnref<SkData> to sk_sp<SkData>.

With the move from SkData::NewXXX to SkData::MakeXXX most
SkAutoTUnref<SkData> were changed to sk_sp<SkData>. However,
there are still a few SkAutoTUnref<SkData> around, so clean
them up.

Review-Url: https://codereview.chromium.org/2212493002
diff --git a/src/codec/SkCodecImageGenerator.h b/src/codec/SkCodecImageGenerator.h
index 6d34223..b125643 100644
--- a/src/codec/SkCodecImageGenerator.h
+++ b/src/codec/SkCodecImageGenerator.h
@@ -38,7 +38,7 @@
     SkCodecImageGenerator(SkCodec* codec, SkData* data);
 
     SkAutoTDelete<SkCodec> fCodec;
-    SkAutoTUnref<SkData> fData;
+    sk_sp<SkData> fData;
 
     typedef SkImageGenerator INHERITED;
 };