Code Cleanup for extension_prefs, as AddDisableReasons() is not required same behavior can be achie…

Code Cleanup for extension_prefs, as AddDisableReasons() is not required same behavior can be achieved by AddDisableReason().

BUG=475911
Committed: https://crrev.com/f5c302712f48ae014617ea242ef49f3e3f757be3
Cr-Commit-Position: refs/heads/master@{#325387}

[Deepak, 2015-04-10 13:19:16]

deepak.m1@samsung.com changed reviewers:
+ yoz@chromium.org

[Deepak, 2015-04-10 13:19:17]

PTAL for this small clean up.
Thanks

[Deepak, 2015-04-13 15:16:24]

PTAL for this small clean up.
Thanks

[Deepak, 2015-04-15 07:19:33]

deepak.m1@samsung.com changed reviewers:
+ rockot@chromium.org

[Deepak, 2015-04-15 07:19:34]

@rockot
PTAL at this small change.

[Ken Rockot(use gerrit already), 2015-04-15 17:09:34]

lgtm

[Deepak, 2015-04-16 02:37:56]

The CQ bit was checked by deepak.m1@samsung.com

[commit-bot: I haz the power, 2015-04-16 02:38:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1073153002/1

[commit-bot: I haz the power, 2015-04-16 03:30:53]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-16 03:31:55]

Patchset 1 (id:??) landed as
https://crrev.com/f5c302712f48ae014617ea242ef49f3e3f757be3
Cr-Commit-Position: refs/heads/master@{#325387}