[NaCl SDK] nacl_io: Fix excess realloc'ing in memfs nodes.

[NaCl SDK] nacl_io: Fix excess realloc'ing in memfs nodes.

This was causes extreme performance issues when
untaring large files in naclports (specifically
with python).

Committed: https://crrev.com/314a240ec3fd6a40f9e2e543fa692eb44d667ab2
Cr-Commit-Position: refs/heads/master@{#295299}

[Sam Clegg, 2014-09-16 18:48:46]

sbc@chromium.org changed reviewers:
+ binji@chromium.org, bradnelson@chromium.org

[bradn, 2014-09-17 16:44:57]

bradnelson@google.com changed reviewers:
+ bradnelson@google.com

[bradn, 2014-09-17 16:44:58]

lgtm

[binji, 2014-09-17 16:49:11]

lgtm

[Sam Clegg, 2014-09-17 17:19:17]

The CQ bit was checked by sbc@chromium.org

[commit-bot: I haz the power, 2014-09-17 17:20:12]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/574803002/40001

[commit-bot: I haz the power, 2014-09-17 18:11:39]

Committed patchset #3 (id:40001) as 5124fbd51d2e765be8d79c8a68ec39c5179746f0

[commit-bot: I haz the power, 2014-09-17 18:12:30]

Patchset 3 (id:??) landed as
https://crrev.com/314a240ec3fd6a40f9e2e543fa692eb44d667ab2
Cr-Commit-Position: refs/heads/master@{#295299}