Move SkPDFStream back to SkStream to save memory.

src/core/SkStreamPriv.h

Index: src/core/SkStreamPriv.h
diff --git a/src/core/SkStreamPriv.h b/src/core/SkStreamPriv.h
index 5b5a73adef0f7368bc6df2159af55e116a9d48fd..13a090c3f377e74ee1b02b904fa6228a6aa0031b 100644
--- a/src/core/SkStreamPriv.h
+++ b/src/core/SkStreamPriv.h
@@ -10,6 +10,7 @@
 
 class SkAutoMalloc;
 class SkStream;
+class SkStreamRewindable;
 class SkData;
 
 /**
@@ -34,4 +35,11 @@ size_t SkCopyStreamToStorage(SkAutoMalloc* storage, SkStream* stream);
  */
 SkData *SkCopyStreamToData(SkStream* stream);
 
+/**
+ *  Attempt to convert this stream to a StreamRewindable in the
+ *  cheapest possible manner (calling duplicate() if possible, and
+ *  otherwise copying to memory).

[reed1, 2014/07/12 11:05:05]

What happens with subsequent reads to the newly returned object? Do they affect
the cursor in the original stream?

[hal.canary, 2014/07/14 14:34:11]

Good question.  Before http://crrev.com/340783013, the PDF backend got a
SkStream from SkTypeface::openStream() and and rewinded it after each read.

+ */
+SkStreamRewindable* SkStreamRewindableFromSkStream(SkStream* stream);
+
 #endif  // SkStreamPriv_DEFINED