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.cpp b/src/image/SkImage.cpp
index 8e46407..15c5ea6 100644
--- a/src/image/SkImage.cpp
+++ b/src/image/SkImage.cpp
@@ -134,7 +134,7 @@
         SkASSERT(defaultSerializer.get());
         effectiveSerializer = defaultSerializer.get();
     }
-    SkAutoTUnref<SkData> encoded(this->refEncoded());
+    sk_sp<SkData> encoded(this->refEncoded());
     if (encoded && effectiveSerializer->useEncodedData(encoded->data(), encoded->size())) {
         return encoded.release();
     }