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/image/SkImage_Gpu.cpp b/src/image/SkImage_Gpu.cpp
index 6cce96c..c795d54 100644
--- a/src/image/SkImage_Gpu.cpp
+++ b/src/image/SkImage_Gpu.cpp
@@ -440,7 +440,7 @@
         // Here we're just using presence of data to know whether there is a codec behind the image.
         // In the future we will access the cacherator and get the exact data that we want to (e.g.
         // yuv planes) upload.
-        SkAutoTUnref<SkData> data(this->refEncoded());
+        sk_sp<SkData> data(this->refEncoded());
         if (!data && !this->peekPixels(nullptr)) {
             return 0;
         }