Revert of Switch SkPDFStream's internal storage from SkStream to SkData

Revert of Switch SkPDFStream's internal storage from SkStream to SkData (https://codereview.chromium.org/340783013/)

Reason for revert:
Causes canary failures

Original issue's description:
> Switch SkPDFStream's internal storage from SkStream to SkData
> 
> Motivation: This makes SkPDFStream thread-safe for two threads
> serializing it at once, since a SkStream has an internal position.
> 
> Updated SkPDFFont, SkPDFGraphicState, and SkPDFPage's use of
> SkPDFStream to use the SkData constructor rather than the SkStream
> constructor (saving a memcpy).
> 
> BUG=skia:2683
> 
> Committed: https://skia.googlesource.com/skia/+/c1dfa14b645ae274780f026dd86c9b633fbdad06

TBR=mtklein@google.com,djsollen@google.com,halcanary@google.com
NOTREECHECKS=true
NOTRY=true
BUG=skia:2683
Committed: https://skia.googlesource.com/skia/+/e1c55869f37bf7c5f365fddc38207dc3ec336b6c

[rmistry, 2014-06-26 21:30:45]

Created Revert of Switch SkPDFStream's internal storage from SkStream to SkData

[commit-bot: I haz the power, 2014-06-26 21:30:57]

CQ is trying da patch. Follow status at
 https://skia-tree-status.appspot.com/cq/rmistry@google.com/354043005/1

[commit-bot: I haz the power, 2014-06-26 21:31:11]

Change committed as e1c55869f37bf7c5f365fddc38207dc3ec336b6c