Fix clobbered register when setting this_function variable.

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}

[rossberg, 2015-06-15 09:43:35]

rossberg@chromium.org changed reviewers:
+ rossberg@chromium.org

[rossberg, 2015-06-15 09:43:35]

lgtm

[Michael Starzinger, 2015-06-15 09:44:26]

The CQ bit was checked by mstarzinger@chromium.org

[commit-bot: I haz the power, 2015-06-15 09:44:38]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1185703002/20001

[commit-bot: I haz the power, 2015-06-15 10:18:50]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-06-15 10:19:05]

Patchset 2 (id:??) landed as
https://crrev.com/bf2bbc8ba508ccd21edf3c08d2e4192c4764ae91
Cr-Commit-Position: refs/heads/master@{#29020}

[Michael Achenbach, 2015-06-15 11:55:48]

A revert of this CL (patchset #2 id:20001) has been created in
https://codereview.chromium.org/1184093003/ by machenbach@chromium.org.

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

[arv (Not doing code reviews), 2015-06-15 16:37:43]

LGTM