Increase Native Client DEPS version to 2500.

BUG=none
TEST=all tests should still pass, especially nacl_ui_tests

Review URL: http://codereview.chromium.org/2814006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@50500 0039d316-1c4b-4281-b951-d872f2087c98

DEPS

@@ -6,7 +6,7 @@ vars = {
   "skia_revision": "582",
   "chromium_git": "http://src.chromium.org/git",
   "swig_revision": "40423",
-  "nacl_revision": "2441",
+  "nacl_revision": "2555",
   "libvpx_revision": "47941",
   "libjingle_revision": "21",
 }