Update V8 to version 4.3.56.

Summary of changes available at:
https://chromium.googlesource.com/v8/v8/+log/c5443d75..b09c6a7d

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
BUG=

Review URL: https://codereview.chromium.org/1005693012

Cr-Commit-Position: refs/heads/master@{#322237}

DEPS

@@ -47,7 +47,7 @@ vars = {
   # the commit queue can handle CLs rolling Skia
   # and V8 without interference from each other.
   'v8_branch': 'trunk',
-  'v8_revision': 'c5443d75a1e3e9b700ba41beea24b8e03fdfd80a',
+  'v8_revision': 'b09c6a7d53380f7db6af2ce3cd61d2db868e335d',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling WebRTC
   # and V8 without interference from each other.