Update V8 to version 5.7.81.

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 26 matching lines @@
   # the commit queue can handle CLs rolling sfntly
   # and whatever else without interference from each other.
   'sfntly_revision': '64f78562d2003eb7cacaaa86a398cbd41881ba6f',
   # 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': 'e18c97b73a0392b2eee57a111122dd5b637e36e6',
   # 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': 'f796cb3f3d633f673ec266f1d5fdd277ab66e967',
+  'v8_revision': '0ef6febcaed3cd200495a0c90ce20306e7e1c14e',
   # 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': 'ebc8dab6f8b8d79ec221c94de39a921145abd404',
   # 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': 'f1a2aefcd8709340d9fde572e2e516fcda928961',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling build tools
@@ skipping 996 matching lines @@
 ]
 
 recursedeps = [
   # buildtools provides clang_format, libc++, and libc++abi
   'src/buildtools',
   # android_tools manages the NDK.
   'src/third_party/android_tools',
   # ANGLE manages DEPS that it also owns the build files for, such as dEQP.
   ("src/third_party/angle", "DEPS.chromium"),
 ]