Roll Webkit DEPS to fix layout test status

BUG=
R=johnniwinther@google.com

Review URL: https://codereview.chromium.org/2134153002 .
diff --git a/tools/deps/dartium.deps/DEPS b/tools/deps/dartium.deps/DEPS
index 6d6dda2..425feca 100644
--- a/tools/deps/dartium.deps/DEPS
+++ b/tools/deps/dartium.deps/DEPS
@@ -9,7 +9,7 @@
 
 vars.update({
   "dartium_chromium_commit": "ef7d4ae18c646aea34c07a7ef62de7342c3b8c12",
-  "dartium_webkit_commit": "5603ae28a2d63db1831e35d702ee0773b5d9734c",
+  "dartium_webkit_commit": "cdd5782d60ee680fb7651afc7525dc371ccaf4c0",
   "chromium_base_revision": "338390",
 
   # We use mirrors of all github repos to guarantee reproducibility and