Update V8 to version 4.5.18.

Update V8 to version 4.5.18.

Summary of changes available at:
https://chromium.googlesource.com/v8/v8/+log/de10b875..51a9312f

Please follow these instructions for assigning/CC'ing issues:
https://code.google.com/p/v8-wiki/wiki/TriagingIssues

TBR=hablich@chromium.org,machenbach@chromium.org,yangguo@chromium.org,vogelheim@chromium.org

[v8-autoroll, 2015-05-27 10:46:39]

The CQ bit was checked by v8-autoroll@chromium.org

[commit-bot: I haz the power, 2015-05-27 10:47:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1154363002/1

[commit-bot: I haz the power, 2015-05-27 11:46:02]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-05-27 11:46:03]

Try jobs failed on following builders:
  win_chromium_compile_dbg_ng on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_comp...)

[Michael Achenbach, 2015-05-27 13:23:04]

On 2015/05/27 11:46:03, I haz the power - commit-bot wrote:
> Try jobs failed on following builders:
>   win_chromium_compile_dbg_ng on tryserver.chromium.win (JOB_FAILED,
>
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_comp...)

Hmm - win compile was expected - the rest is new...

[Michael Achenbach, 2015-05-27 13:23:43]

The CQ bit was checked by machenbach@chromium.org

[commit-bot: I haz the power, 2015-05-27 13:23:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1154363002/1

[Michael Achenbach, 2015-05-27 13:33:24]

Bisect job https://codereview.chromium.org/1152553004/

[Michael Achenbach, 2015-05-27 14:03:18]

On 2015/05/27 13:33:24, Michael Achenbach wrote:
> Bisect job https://codereview.chromium.org/1152553004/

Bisect points to this:
https://chromium.googlesource.com/v8/v8/+/28cea2b749f24ba33e6e0c8e343dd0d6258...

[commit-bot: I haz the power, 2015-05-27 14:14:15]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-05-27 14:14:15]

Try jobs failed on following builders:
  win_chromium_compile_dbg_ng on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_comp...)