Update WebKit to r123970.

BUG=none
TEST=none
TBR=tomhudson
Review URL: https://chromiumcodereview.appspot.com/10830062

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@148901 0039d316-1c4b-4281-b951-d872f2087c98

DEPS

@@ -8,7 +8,7 @@ vars = {
   "sourceforge_url": "http://%(repo)s.svn.sourceforge.net/svnroot/%(repo)s",
   "webkit_trunk": "http://svn.webkit.org/repository/webkit/trunk",
   "nacl_trunk": "http://src.chromium.org/native_client/trunk",
-  "webkit_revision": "123957",
+  "webkit_revision": "123970",
   "chromium_git": "http://git.chromium.org/git",
   "chromiumos_git": "http://git.chromium.org/chromiumos",
   "swig_revision": "69281",