Update V8 to version 4.6.57.

Update V8 to version 4.6.57.

Summary of changes available at:
https://chromium.googlesource.com/v8/v8/+log/b531751e..38a68d3b

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/

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

Committed: https://crrev.com/6d6342b231ef733ac420488fa326f442b5e0dfb4
Cr-Commit-Position: refs/heads/master@{#342401}

[v8-autoroll, 2015-08-07 17:32:15]

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

[commit-bot: I haz the power, 2015-08-07 17:33:07]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1282563002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1282563002/1

[commit-bot: I haz the power, 2015-08-07 19:14:40]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-07 19:15:31]

Patchset 1 (id:??) landed as
https://crrev.com/6d6342b231ef733ac420488fa326f442b5e0dfb4
Cr-Commit-Position: refs/heads/master@{#342401}