Update V8 to version 4.9.56.

Update V8 to version 4.9.56.

Summary of changes available at:
https://chromium.googlesource.com/v8/v8/+log/6ed50d99..b787e6bc

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

Please close rolling in case of a roll revert:
https://v8-roll.appspot.com/
This only works with a Google account.

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

Committed: https://crrev.com/6b7eb2806a47da3e2f086c078519d0b8ab6916ac
Cr-Commit-Position: refs/heads/master@{#361326}

[v8-autoroll, 2015-11-24 07:17:10]

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

[commit-bot: I haz the power, 2015-11-24 07:17:24]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1467413003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1467413003/1

[commit-bot: I haz the power, 2015-11-24 08:52:44]

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

[commit-bot: I haz the power, 2015-11-24 08:52:45]

Try jobs failed on following builders:
  linux_android_rel_ng on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_android_r...)

[Michael Hablich, 2015-11-24 09:08:28]

The CQ bit was checked by hablich@chromium.org

[commit-bot: I haz the power, 2015-11-24 09:09:01]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1467413003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1467413003/1

[commit-bot: I haz the power, 2015-11-24 12:29:30]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-11-24 12:30:24]

Patchset 1 (id:??) landed as
https://crrev.com/6b7eb2806a47da3e2f086c078519d0b8ab6916ac
Cr-Commit-Position: refs/heads/master@{#361326}