Handle SkStream::rewind properly.

include/core/SkStream.h

Index: include/core/SkStream.h
diff --git a/include/core/SkStream.h b/include/core/SkStream.h
index d7a105d3b84e1080fdc4157b1d40f52a1c68750c..a81a9d5b80bc7f6a7473db840e8fd89865c2b7f8 100644
--- a/include/core/SkStream.h
+++ b/include/core/SkStream.h
@@ -96,7 +96,9 @@ public:
     SkData* readData();
 
 //SkStreamRewindable
-    /** Rewinds to the beginning of the stream. If this cannot be done, return false. */
+    /** Rewinds to the beginning of the stream. Returns false iff after this call the stream
+     *  is NOT at the beginning.

[bungeman-skia, 2013/08/26 22:24:58]

I like this, but it means that this default implementation doesn't satisfy the
requirements. Maybe

Rewinds to the beginning of the stream. The current position is not affected
when false is returned.

Returns false iff one or both of the following is true:
  * the stream is known to be not at the beginning upon return
  * the stream is not known to be at the beginning upon return

[scroggo, 2013/08/27 19:49:26]

I modified these because a slight movement of the word 'not' might be confusing
(especially for someone who doesn't speak English as their first language). I
also don't think they can both be true. Here's what I wrote:

Returns false iff after this call one of the following is true:
 * The stream is known to be somewhere other than the beginning.
 * It is unknown whether the stream is at the beginning.

Let me know what you think.

+     */
     virtual bool rewind() { return false; }
 
     /** Duplicates this stream. If this cannot be done, returns NULL.