Add GYP_CHROMIUM_NO_ACTION environment variable to gyp_chromium

This is inorder to allow non-standard bots to run gclient runhooks without
running gyp_chromium.

See also: https://codereview.chromium.org/69173006/

R=brettw@chromium.org, mkosiba@chromium.org
BUG=

Review URL: https://codereview.chromium.org/76403005

git-svn-id: http://src.chromium.org/svn/trunk/src/build@236300 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

gyp_chromium

@@ -82,6 +82,10 @@ def additional_include_files(args=[]):
 if __name__ == '__main__':
   args = sys.argv[1:]
 
+  if int(os.environ.get('GYP_CHROMIUM_NO_ACTION', 0)):
+    print 'Skipping gyp_chromium due to GYP_CHROMIUM_NO_ACTION env var.'
+    sys.exit(0)
+
   # Use the Psyco JIT if available.
   if psyco:
     psyco.profile()