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..2091c765df37c12cb8e6ea608f221dcb73466e9e 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 true iff the stream is rewindable
+     *  and after this call the stream is at the beginning.

[scroggo, 2013/08/26 20:44:31]

Per discussion with Ben, I modified this comment to allow streams that fail to
rewind sometimes.

The goal here is to prevent a stream implementation from saying "I failed to
rewind because I was already at the beginning." I further stated that the stream
must be rewindable so that non-rewindable streams need not return true when they
are at the beginning.

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