Update V8 to version 4.5.56.

Update V8 to version 4.5.56.

Summary of changes available at:
https://chromium.googlesource.com/v8/v8/+log/fffc68e8..cb392cb0

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

Committed: https://crrev.com/a08e761a4a4f5c863682a39e234b4ca3af170159
Cr-Commit-Position: refs/heads/master@{#334571}

[v8-autoroll, 2015-06-16 00:46:40]

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

[commit-bot: I haz the power, 2015-06-16 00:47:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1182893005/1

[commit-bot: I haz the power, 2015-06-16 03:23:48]

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

[commit-bot: I haz the power, 2015-06-16 03:23:49]

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

[Michael Achenbach, 2015-06-16 06:55:00]

The CQ bit was checked by machenbach@chromium.org

[commit-bot: I haz the power, 2015-06-16 06:55:04]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1182893005/1

[commit-bot: I haz the power, 2015-06-16 09:13:36]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-16 09:14:33]

Patchset 1 (id:??) landed as
https://crrev.com/a08e761a4a4f5c863682a39e234b4ca3af170159
Cr-Commit-Position: refs/heads/master@{#334571}

[Zhenyao Mo, 2015-06-16 16:57:46]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1189863003/ by zmo@chromium.org.

The reason for reverting is: Broke WebGL 2 conformance tests

Fatal error in ../../v8/src/ic/stub-cache.h, line 111
# Check failed: name->HasHashCode().

build chrome, run with --enable-unsafe-es3-apis

goto
https://www.khronos.org/registry/webgl/sdk/tests/webgl-conformance-tests.html

select Version 2.0.0 (beta) in the dropbox, and run samplerobejct.html (may need
to run twice).