Update V8 to version 5.1.56.

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 25 matching lines @@
   # the commit queue can handle CLs rolling sfntly
   # and whatever else without interference from each other.
   'sfntly_revision': '130f832eddf98467e6578b548cb74ce17d04a26d',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling Skia
   # and whatever else without interference from each other.
   'skia_revision': 'a5ab9ec295b2e6dca166775a98db67a9a8c18c37',
   # 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': 'f31c787725eb23f0771a8c98821fe240dcb534a8',
+  'v8_revision': '9af7f428313494cbb7a75e99fcf0fc636f37b0f0',
   # 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': 'df6e95e7669883c8fe9ef956c69a544154701a49',
   # 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': '9cb1df4f4b34e53e5f37d6c99857a6fb8c8f360d',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling build tools
@@ skipping 784 matching lines @@
         'src/tools',
     ],
   },
   {
     # A change to a .gyp, .gypi, or to GYP itself should run the generator.
     'name': 'gyp',
     'pattern': '.',
     'action': ['python', 'src/build/gyp_chromium'],
   },
 ]