change SkStreams to work with sk_sp<SkData> instead of SkData*

tests/PictureTest.cpp

Index: tests/PictureTest.cpp
diff --git a/tests/PictureTest.cpp b/tests/PictureTest.cpp
index 7b187b44099820d82529ff2be5d64d6c3a13811d..6ab57c04d741a207fb92f6fe9ab3ba7522c3b8ca 100644
--- a/tests/PictureTest.cpp
+++ b/tests/PictureTest.cpp
@@ -632,7 +632,7 @@ static sk_sp<SkData> serialized_picture_from_bitmap(const SkBitmap& bitmap) {
     SkAutoTUnref<SkPixelSerializer> serializer(
             SkImageEncoder::CreatePixelSerializer());
     picture->serialize(&wStream, serializer);
-    return sk_sp<SkData>(wStream.copyToData());
+    return wStream.detachAsData();
 }
 
 struct ErrorContext {
@@ -670,7 +670,7 @@ DEF_TEST(Picture_EncodedData, reporter) {
     if (!SkImageEncoder::EncodeStream(&wStream, original, SkImageEncoder::kPNG_Type, 100)) {
         return;
     }
-    sk_sp<SkData> data(wStream.copyToData());
+    sk_sp<SkData> data = wStream.detachAsData();
 
     SkBitmap bm;
     bool installSuccess = SkDEPRECATED_InstallDiscardablePixelRef(data.get(), &bm);