Move SkPDFStream back to SkStream to save memory.

src/core/SkStreamPriv.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkStreamPriv_DEFINED
 #define SkStreamPriv_DEFINED
 
 class SkAutoMalloc;
 class SkStream;
+class SkStreamRewindable;
 class SkData;
 
 /**
  *  Copy the provided stream to memory allocated by storage.
  *  Used by SkImageDecoder_libbmp and SkImageDecoder_libico.
  *  @param storage Allocator to hold the memory. Will be reset to be large
  *      enough to hold the entire stream. Upon successful return,
  *      storage->get() will point to data holding the SkStream's entire
  *      contents.
  *  @param stream SkStream to be copied into storage.
  *  @return size_t Total number of bytes in the SkStream, which is also the
  *      number of bytes pointed to by storage->get(). Returns 0 on failure.
  */
 size_t SkCopyStreamToStorage(SkAutoMalloc* storage, SkStream* stream);
 
 /**
  *  Copy the provided stream to an SkData variable.
  *  @param stream SkStream to be copied into data.
  *  @return SkData* The resulting SkData after the copy. This data
  *      will have a ref count of one upon return and belongs to the
  *      caller. Returns NULL on failure.
  */
 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