Revert of [Autofill Clean up] Revert changes introduced by Autocheckout to autofill

Revert of [Autofill Clean up] Revert changes introduced by Autocheckout to autofill (patchset #1 id:1 of https://codereview.chromium.org/609733003/)

Reason for revert:
these changes are still necessary for requestAutocomplete

Original issue's description:
> [Autofill Clean up] Revert changes introduced by Autocheckout to autofill
> disabled and readonly fields. Autocheckout is deprecated.
>
> R=isherman@chromium.org
> BUG=231160
>
> Committed: https://crrev.com/d9b040ba4ff2ff78f183816b9d0e34c5f450160c
> Cr-Commit-Position: refs/heads/master@{#297015}

TBR=isherman@chromium.org,ziran.sun@samsung.com
NOTREECHECKS=true
NOTRY=true
BUG=231160
Committed: https://crrev.com/33199a111975498bb568c605dd1173cc0bbe9db6
Cr-Commit-Position: refs/heads/master@{#299331}

[Evan Stade, 2014-10-13 18:35:09]

Created Revert of [Autofill Clean up] Revert changes introduced by Autocheckout
to autofill

[commit-bot: I haz the power, 2014-10-13 18:36:12]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/648243003/1

[commit-bot: I haz the power, 2014-10-13 18:39:18]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-13 18:40:11]

Patchset 1 (id:??) landed as
https://crrev.com/33199a111975498bb568c605dd1173cc0bbe9db6
Cr-Commit-Position: refs/heads/master@{#299331}