Update V8 to version 4.9.78.

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': 'f15246320cf69cd7bcd8882601c67eddc655d9ba',
   # 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': 'f61d9a28e720fa0a3c60e0614d579010df70e501',
+  'v8_revision': '677e47975e62ddb8bee254676bbe920c996eeb48',
   # 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': 'df99a00d96fae932bae824dccba13156bf7eddd0',
   # 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': '847638a64a32df1b357b57507170301195263a1c',
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling build tools
@@ skipping 753 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'],
   },
 ]