return and take SkImageGenerator as unique_ptr

BUG=skia:

Change-Id: I4bc11042dd1dbf1eabd40af206027bc65acc3186
Reviewed-on: https://skia-review.googlesource.com/8444
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Matt Sarett <msarett@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
diff --git a/src/codec/SkCodecImageGenerator.h b/src/codec/SkCodecImageGenerator.h
index d771f49..727a747 100644
--- a/src/codec/SkCodecImageGenerator.h
+++ b/src/codec/SkCodecImageGenerator.h
@@ -18,10 +18,7 @@
      * If this data represents an encoded image that we know how to decode,
      * return an SkCodecImageGenerator.  Otherwise return nullptr.
      */
-    static SkImageGenerator* NewFromEncodedCodec(sk_sp<SkData>);
-    static SkImageGenerator* NewFromEncodedCodec(SkData* data) {
-        return NewFromEncodedCodec(sk_ref_sp(data));
-    }
+    static std::unique_ptr<SkImageGenerator> MakeFromEncodedCodec(sk_sp<SkData>);
 
 protected:
     SkData* onRefEncodedData(GrContext* ctx) override;