Update V8 to version 5.4.175.

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 22 matching lines @@
   # the commit queue can handle CLs rolling sfntly
   # and whatever else without interference from each other.
   'sfntly_revision': '468cad540fa1b0027cad60456f53feabecdce2bc',
   # 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': 'eaf6d4102258c867b3101aadfbd6ffb9d17d429e',
   # 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': '946f9cc0a447316ea8f66af62ea7f06abe788ac2',
+  'v8_revision': 'db4ff0ae0756e276e676d2464e040245aec8a83d',
   # 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': '7f63a272f7d9785ce41b6d10bb3106c49a968e57',
   # 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': '4c32feb1940a8e9a11e48f916176e84dfa3f01d6',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling build tools
@@ skipping 900 matching lines @@
   {
     # A change to a .gyp, .gypi, or to GYP itself should run the generator.
     'name': 'gyp',
     'pattern': '.',
     'action': ['python', 'src/build/gyp_chromium', '--running-as-hook'],
   },
 ]
 
 # ANGLE manages DEPS that it also owns the build files for, such as dEQP.
 recursedeps = [("src/third_party/angle", "DEPS.chromium")]