SkData to SkStreamAsset to avoid unneeded copying

dm/DMPDFRasterizeTask.h

Index: dm/DMPDFRasterizeTask.h
diff --git a/dm/DMPDFRasterizeTask.h b/dm/DMPDFRasterizeTask.h
index 2cc1ef70dabdbe4a877544b7ac31df4f0e1c512c..d5d983c936300535b95b68d0631eb70409cf1aca 100644
--- a/dm/DMPDFRasterizeTask.h
+++ b/dm/DMPDFRasterizeTask.h
@@ -21,8 +21,9 @@ 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;
@@ -31,7 +32,7 @@ public:
 
 private:
     const SkString fName;
-    SkAutoTUnref<SkData> fPdf;
+    SkAutoTUnref<SkStreamAsset> fPdf;
     RasterizePdfProc fRasterize;
 };