SkDynamicMemoryWStream::detachAsStream() returns unique_ptr

https://crrev.com/2747183002 must land first.
Change-Id: I65d1285a24d63c2c2f18662d511dea1c399511e1
Reviewed-on: https://skia-review.googlesource.com/9682
Commit-Queue: Hal Canary <halcanary@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
diff --git a/include/core/SkStream.h b/include/core/SkStream.h
index 8df59af..0a53d47 100644
--- a/include/core/SkStream.h
+++ b/include/core/SkStream.h
@@ -383,7 +383,7 @@
     sk_sp<SkData> detachAsData();
 
     /** Reset, returning a reader stream with the current content. */
-    SkStreamAsset* detachAsStream();
+    std::unique_ptr<SkStreamAsset> detachAsStream();
 
     /** Reset the stream to its original, empty, state. */
     void reset();