SkData to SkStreamAsset to avoid unneeded copying

dm/DMPDFRasterizeTask.h

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef DMPDFRasterizeTask_DEFINED
 #define DMPDFRasterizeTask_DEFINED
 
 #include "DMTask.h"
 #include "SkBitmap.h"
 #include "SkData.h"
 #include "SkStream.h"
 #include "SkString.h"
 #include "SkTemplates.h"
 
 namespace DM {
 
 typedef bool (*RasterizePdfProc)(SkStream* pdf, SkBitmap* output);
 
 class PDFRasterizeTask : public CpuTask {
 public:
+    // takes ownership of SkStreamAsset.

[mtklein, 2014/08/25 21:44:33]

I'm finding this hard to think about.

Can we not just use SkRef and SkAutoTUnref as normal?

If you need to pass exclusive SkStreamAssets around, let's do that consistently
everywhere and use SkAutoTDelete instead of SkAutoTUnref.

[hal.canary, 2014/08/26 15:20:50]

SkStreams should not be reference counted, since it doesn't make sense to share
them.  Ask Ben about his attempt to change that.
It doesn't make sense because we are asking for exclusive ownership.  I do this
on every function I write that takes a SkStream and produces a possibly
long-lived object.  And I always note this in the documentation.
 
I would be happy with that change, but the last time I tried that, the reviewer
asked me to change it back to AutoUnref.

[mtklein, 2014/08/26 15:30:54]

Gotcha.  Let's make it SkAutoTDelete then.  Your explanation says that's the
right thing to do.

     PDFRasterizeTask(const Task& parent,
-                     SkData* pdf,
+                     SkStreamAsset* pdf,
                      RasterizePdfProc);
 
     virtual void draw() SK_OVERRIDE;
     virtual bool shouldSkip() const SK_OVERRIDE { return NULL == fRasterize; }
     virtual SkString name()   const SK_OVERRIDE { return fName; }
 
 private:
     const SkString fName;
-    SkAutoTUnref<SkData> fPdf;
+    SkAutoTUnref<SkStreamAsset> fPdf;
     RasterizePdfProc fRasterize;
 };
 
 }  // namespace DM
 
 #endif  // DMPDFRasterizeTask_DEFINED