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

Please reply to the V8 sheriff danno@chromium.org in case of problems.

TBR=danno@chromium.org

Review URL: https://codereview.chromium.org/288193003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@270987 0039d316-1c4b-4281-b951-d872f2087c98

DEPS

@@ -56,7 +56,7 @@ vars = {
   # 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.