Sync app order for extension items

Sync app order for extension items

This restores syncing app order using the extensions sync to keep ToT
behavior in better shape.

BUG=306945
R=jennyz@chromium.org, xiyuan@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=229971

[stevenjb, 2013-10-19 01:15:20]

In the interest in reducing the pressure for working out how we are going to
sync the app list going forward, this should allow us to continue syncing the
model the "old way" in the interim.

Note: until we implement the new sync model, any folders will show up at either
the end or the beginning, depending on how we implement their GetSortOrder()
method.

[xiyuan, 2013-10-21 16:36:11]

lgtm

[jennyz, 2013-10-21 16:42:49]

lgtm

[commit-bot: I haz the power, 2013-10-21 17:41:25]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/stevenjb@chromium.org/29613004/30001

[commit-bot: I haz the power, 2013-10-22 00:19:52]

Retried try job too often on win7_aura for step(s) browser_tests
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win7_aura&...

[stevenjb, 2013-10-22 00:23:54]

Committed patchset #3 manually as r229971 (presubmit successful).