Revert of Disable delaying of Apps installation on Chrome OS for first time sign-in

Revert of Disable delaying of Apps installation on Chrome OS for first time sign-in (patchset #1 id:1 of https://codereview.chromium.org/931663007/)

Reason for revert:
Seems to have broken PDFExtensionTest, blocking Blink rolls. See crbug.com/460328.

Original issue's description:
> Disable delaying of Apps installation on Chrome OS for first time sign-in
>
> This behavior is introduced by a772ed62ff0641df984feffe977b1545e94d53f1.
> It makes ExternalPrefLoader not being ready when user sign in to Chromebook for
> the first time and accidentally blocks all installation of external extensions
> if Chrome Sync is turned off, including force installed extensions by policy.
>
> BUG=457539
> TEST=manual
>
> Committed: https://crrev.com/9a5194c07bd95febb99e61cdaaf9e42e602bd0be
> Cr-Commit-Position: refs/heads/master@{#317074}

TBR=nkostylev@chromium.org,asargent@chromium.org,kalman@chromium.org,binjin@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=457539
Committed: https://crrev.com/8476015c8a209afc3a75dcaf97e09f98d271d7cc
Cr-Commit-Position: refs/heads/master@{#317214}

[Ken Russell (switch to Gerrit), 2015-02-20 01:42:47]

Created Revert of Disable delaying of Apps installation on Chrome OS for first
time sign-in

[commit-bot: I haz the power, 2015-02-20 01:43:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/939183003/1

[commit-bot: I haz the power, 2015-02-20 01:44:33]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-20 01:45:14]

Patchset 1 (id:??) landed as
https://crrev.com/8476015c8a209afc3a75dcaf97e09f98d271d7cc
Cr-Commit-Position: refs/heads/master@{#317214}