Update V8 to version 3.19.12.1.

DEPS

 # When adding a new dependency, please update the top-level .gitignore file
 # to list the dependency's destination directory.
 
 vars = {
   # Use this googlecode_url variable only if there is an internal mirror for it.
   # If you do not know, use the full path while defining your new deps entry.
   "googlecode_url": "http://%s.googlecode.com/svn",
   "sourceforge_url": "http://%(repo)s.svn.sourceforge.net/svnroot/%(repo)s",
   "webkit_trunk": "http://src.chromium.org/blink/trunk",
   "nacl_trunk": "http://src.chromium.org/native_client/trunk",
@@ skipping 15 matching lines @@
   # These two FFmpeg variables must be updated together.  One is used for SVN
   # checkouts and the other for Git checkouts.
   "ffmpeg_revision": "203786",
   "ffmpeg_hash": "245a8c0cdfdd5ab3da9045089661017e9ddd8d0e",
 
   "sfntly_revision": "134",
   "skia_revision": "9484",
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling Skia
   # and V8 without interference from each other.
-  "v8_revision": "15040",
+  "v8_revision": "15051",
   # 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": "4197",
   "jsoncpp_revision": "248",
   "nss_revision": "204056",
   # Three lines of non-changing comments so that
   # the commit queue can handle CLs rolling swarm_client
   # and whatever else without interference from each other.
   "swarm_revision": "204510",
@@ skipping 629 matching lines @@
     # A change to a .gyp, .gypi, or to GYP itself should run the generator.
     "pattern": ".",
     "action": ["python", "src/build/gyp_chromium"],
   },
   {
     # Check for landmines (reasons to clobber the build).
     "pattern": ".",
     "action": ["python", "src/build/landmines.py"],
   },
 ]