Update V8 to version 3.27.4 (based on bleeding_edge revision r21317).

DEPS

 # This file is automatically processed to create .DEPS.git which is the file
 # that gclient uses under git.
 #
 # See http://code.google.com/p/chromium/wiki/UsingGit
 #
 # To test manually, run:
 #   python tools/deps2git/deps2git.py -o .DEPS.git -w <gclientdir>
 # where <gcliendir> is the absolute path to the directory containing the
 # .gclient file (the parent of "src").
 #
@@ skipping 38 matching lines @@
   "ffmpeg_hash": "d3a060bd1d6a4f43e9bc7d07f193b0513df4f244",
 
   "sfntly_revision": "228",
   "lighttpd_revision": "33737",
   "skia_revision": "14688",
   "skia_hash": "24f6e29fc133f1082c73e2a96f30bee92e3123aa",
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling Skia
   # and V8 without interference from each other.
   "v8_branch": "trunk",
-  "v8_revision": "21152",
+  "v8_revision": "21318",
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling WebRTC
   # and V8 without interference from each other.
   "webrtc_revision": "6116",
   "jsoncpp_revision": "248",
   "nss_revision": "267366",
   # 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": "ae8085b09e6162b4ec869e430d7d09c16b32b433",
@@ skipping 698 matching lines @@
                 "-s", "src/build/linux/bin/eu-strip.sha1",
     ],
   },
   {
     # A change to a .gyp, .gypi, or to GYP itself should run the generator.
     "name": "gyp",
     "pattern": ".",
     "action": ["python", "src/build/gyp_chromium"],
   },
 ]