Update V8 to version 4.5.56.

DEPS

 # This file is used to manage the dependencies of the Chromium src repo. It is
 # used by gclient to determine what version of each dependency to check out, and
 # where.
 #
 # For more information, please refer to the official documentation:
 #   https://sites.google.com/a/chromium.org/dev/developers/how-tos/get-the-code
 #
 # When adding a new dependency, please update the top-level .gitignore file
 # to list the dependency's destination directory.
 #
@@ skipping 20 matching lines @@
   # If you do not know, use the full path while defining your new deps entry.
   'googlecode_url': 'http://%s.googlecode.com/svn',
   'webkit_revision': 'cd11a0efb00f8e6f94cbe733b72dc138b4f8ef10', # from svn revision 197136
   'chromium_git': 'https://chromium.googlesource.com',
   'libvpx_revision': 'db3f34772338a7e02fc5a7fb9da4d72de68e71b9',
   'sfntly_revision': '1bdaae8fc788a5ac8936d68bf24f37d977a13dac',
   'skia_revision': '5cf19498f9455e4aa8685a9d7775fefe42deb22b',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling V8
   # and whatever else without interference from each other.
-  'v8_revision': 'fffc68e8cae31678d198db13d72f92632b825bf5',
+  'v8_revision': 'cb392cb03a1d4ac89b6c1b8a67af9ea2740613f8',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling swarming_client
   # and whatever else without interference from each other.
   'swarming_revision': 'b39a448d8522392389b28f6997126a6ab04bfe87',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling ANGLE
   # and whatever else without interference from each other.
   'angle_revision': '3975ddec952c8910e0854d0b40c0f96955b018fb',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling build tools
@@ skipping 727 matching lines @@
     # migration completes (let's say Sep 1 2014).
     'name': 'check_git_config',
     'pattern': '.',
     'action': [
         'python',
         'src/tools/check_git_config.py',
         '--running-as-hook',
     ],
   },
 ]