presubmit: unblacklist third_party/WebKit

The current DEFAULT_BLACKLIST in presubmit_support blacklists by
default third_party/.* in every repo. This requires an adjustement
after the blink merge, as it causing all the blink presubmits to
become noops.

BUG=539768

Review URL: https://codereview.chromium.org/1382993004

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@297030 0039d316-1c4b-4281-b951-d872f2087c98

presubmit_support.py

@@ -245,7 +245,8 @@ class InputApi(object):
   DEFAULT_BLACK_LIST = (
       r"testing_support[\\\/]google_appengine[\\\/].*",
       r".*\bexperimental[\\\/].*",
-      r".*\bthird_party[\\\/].*",
+      # Exclude third_party/.* but NOT third_party/WebKit (crbug.com/539768).
+      r".*\bthird_party[\\\/](?!WebKit[\\\/]).*",
       # Output directories (just in case)
       r".*\bDebug[\\\/].*",
       r".*\bRelease[\\\/].*",