Tidy ELF section rewriting internal interface.

Tidy ELF section rewriting internal interface.

Change section data rewriter internal interface to take a section
directly, rather than a pointer to section data.  Remove some of
the more confusing instances of data pointers being passed between
pack and unpack functions.

Readability only.  No behavioural effects.

BUG=385553
Committed: https://crrev.com/1203993ae31ae13a96b935ed3638afe378095576
Cr-Commit-Position: refs/heads/master@{#301347}

[simonb (inactive), 2014-10-24 17:36:02]

simonb@chromium.org changed reviewers:
+ rmcilroy@chromium.org

[rmcilroy, 2014-10-27 10:39:23]

lgtm, thanks.

[simonb (inactive), 2014-10-27 11:28:14]

The CQ bit was checked by simonb@chromium.org

[commit-bot: I haz the power, 2014-10-27 11:28:54]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/650293006/1

[commit-bot: I haz the power, 2014-10-27 12:12:24]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-27 12:12:59]

Patchset 1 (id:??) landed as
https://crrev.com/1203993ae31ae13a96b935ed3638afe378095576
Cr-Commit-Position: refs/heads/master@{#301347}