add helpers for using SkData with picture serialization

samplecode/GMSampleView.cpp

Index: samplecode/GMSampleView.cpp
diff --git a/samplecode/GMSampleView.cpp b/samplecode/GMSampleView.cpp
index 5e48391787bdab8190d3c6af78905e0ec053928c..19cbcc8b5763abc6a20222cf6572b41f5e0ea949 100644
--- a/samplecode/GMSampleView.cpp
+++ b/samplecode/GMSampleView.cpp
@@ -47,12 +47,8 @@ bool GMSampleView::onEvent(const SkEvent& evt) {
 }
 
 #include "SkPicture.h"
-#include "SkStream.h"
 static sk_sp<SkPicture> round_trip_serialize(SkPicture* src) {
-    SkDynamicMemoryWStream stream;
-    src->serialize(&stream);
-    SkAutoTDelete<SkStream> reader(stream.detachAsStream());
-    return SkPicture::MakeFromStream(reader);
+    return SkPicture::MakeFromData(src->serialize().get());
 }
 
 #include "SkPictureRecorder.h"