Update to latest WebKit changes:

tools/deps/dartium.deps/DEPS

 # The file DEPS.chromium from this directory (tools/deps/dartium.deps) is
 # copied into this file, rather than imported, because the new DEPS syntax
 # analyzer does not support the way that we import it.
 # Please keep the code between here and "END OF IMPORTED CHROMIUM DEPS"
 # an exact copy of the modified DEPS.chromium in this directory.
 
 vars = {
   # Start of Dartium vars
 
-  "dartium_chromium_commit": "0612beaf1bf21d11b1af52d4c9977caa4c641146",
+  "dartium_chromium_commit": "aa424e93dc062d902d80db3e5e28c8b309f39403",
   "chromium_base_revision": "378081",
 
   # We use mirrors of all github repos to guarantee reproducibility and
   # consistency between what users see and what the bots see.
   # We need the mirrors to not have 100+ bots pulling github constantly.
   # We mirror our github repos on chromium git servers.
   # DO NOT use this var if you don't see a mirror here:
   #   https://chromium.googlesource.com/
   # named like:
   #   external/github.com/dart-lang/NAME
@@ skipping 923 matching lines @@
   'native_client_sdk',
   'out',
   'sdch',
   'skia',
   'testing',
   'v8',
   'win8'
 ]
 
 # END OF IMPORTED CHROMIUM DEPS