Revert of Fix clobbered register when setting this_function variable.

Revert of Fix clobbered register when setting this_function variable. (patchset #2 id:20001 of https://codereview.chromium.org/1185703002/)

Reason for revert:
[Sheriff] Makes mjsunit/es6/block-const-assign flaky, e.g.:
http://build.chromium.org/p/client.v8/builders/V8%20Linux/builds/4082

Original issue's description:
> Fix clobbered register when setting this_function variable.
>
> R=arv@chromium.org
> TEST=mjsunit/regress/regress-crbug-498022
> BUG=chromium:498022
> LOG=N
>
> Committed: https://crrev.com/bf2bbc8ba508ccd21edf3c08d2e4192c4764ae91
> Cr-Commit-Position: refs/heads/master@{#29020}

TBR=arv@chromium.org,rossberg@chromium.org,mstarzinger@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:498022
Committed: https://crrev.com/06ac599d1ed7c3f309d74686eefdedfca6decf73
Cr-Commit-Position: refs/heads/master@{#29022}

[Michael Achenbach, 2015-06-15 11:55:49]

Created Revert of Fix clobbered register when setting this_function variable.

[commit-bot: I haz the power, 2015-06-15 11:55:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1184093003/1

[commit-bot: I haz the power, 2015-06-15 11:56:15]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-15 11:56:34]

Patchset 1 (id:??) landed as
https://crrev.com/06ac599d1ed7c3f309d74686eefdedfca6decf73
Cr-Commit-Position: refs/heads/master@{#29022}