WebKit Roll 56306:56312.

TBR=dpranke
TEST=rarely
BUG=verily

Review URL: http://codereview.chromium.org/1142006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@42192 0039d316-1c4b-4281-b951-d872f2087c98

DEPS

 vars = {
   "webkit_trunk":
     "http://svn.webkit.org/repository/webkit/trunk",
-  "webkit_revision": "56306",
+  "webkit_revision": "56312",
   "ffmpeg_revision": "42082",
   "skia_revision": "504",
   "chromium_git": "http://src.chromium.org/git",