Revert of Use in-object fields instead of private symbols for regexp slots.

Revert of Use in-object fields instead of private symbols for regexp slots. (patchset #4 id:60001 of https://codereview.chromium.org/1428203003/ )

Reason for revert:
A clean revert of https://codereview.chromium.org/1419823010/ was not possible because of this CL. Thus, I am also reverting this CL.

Original issue's description:
> Use in-object fields instead of private symbols for regexp slots.
>
> R=bmeurer@chromium.org
>
> Committed: https://crrev.com/5a1e42c039ac3379ebe1e7e34fb8163e1ec1493e
> Cr-Commit-Position: refs/heads/master@{#31791}

TBR=bmeurer@chromium.org,yangguo@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Committed: https://crrev.com/626fd5f0b9269011124d0bc1b14348502c029872
Cr-Commit-Position: refs/heads/master@{#31800}

[Michael Hablich, 2015-11-04 18:32:18]

Created Revert of Use in-object fields instead of private symbols for regexp
slots.

[commit-bot: I haz the power, 2015-11-04 18:32:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1421593009/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1421593009/1

[commit-bot: I haz the power, 2015-11-04 18:32:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1421593009/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1421593009/1

[commit-bot: I haz the power, 2015-11-04 18:32:57]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-04 18:33:33]

Patchset 1 (id:??) landed as
https://crrev.com/626fd5f0b9269011124d0bc1b14348502c029872
Cr-Commit-Position: refs/heads/master@{#31800}