Only enforce the 'chromium' check in MB for the default config file.

tools/mb/mb_unittest.py

 #!/usr/bin/python
 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Tests for mb.py."""
 
 import json
 import StringIO
 import os
@@ skipping 162 matching lines @@
     'rel': {
       'gn_args': 'is_debug=false',
     },
   },
   'private_configs': ['private'],
   'unsupported_configs': ['unsupported'],
 }
 """
 
 
 TEST_BAD_CONFIG_ERR = """\

[DaleCurtis, 2016/03/16 16:42:22]

It doesn't look like this is used anymore; remove?

 mb config file /fake_src/tools/mb/mb_config.pyl has problems:
   Config "gn_rel_bot_1" used by a bot is also listed in "common_dev_configs".
   Unknown config "unsupported" referenced from "unsupported_configs".
   Unknown config "private" referenced from "private_configs".
   Public artifact builder "a" can not contain the "chrome_with_codecs" mixin.
   Public artifact builder "b" can not contain the "chrome_with_codecs" mixin."""
 
 
 class UnitTest(unittest.TestCase):
   def fake_mbw(self, files=None, win32=False):
     mbw = FakeMBW(win32=win32)
     mbw.files.setdefault(mbw.default_config, TEST_CONFIG)
     if files:
       for path, contents in files.items():
         mbw.files[path] = contents
     return mbw
 
-  def check(self, args, mbw=None, files=None, out=None, err=None, ret=None,
-            exception=None):
+  def check(self, args, mbw=None, files=None, out=None, err=None, ret=None):
     if not mbw:
       mbw = self.fake_mbw(files)
-    mbw.ParseArgs(args)
 
-    actual_ret = None
-    if exception is not None:
-      self.assertRaisesRegexp(Exception, exception, mbw.args.func)
-    else:
-      actual_ret = mbw.args.func()
+    actual_ret = mbw.Main(args)
 
     self.assertEqual(actual_ret, ret)
     if out is not None:
       self.assertEqual(mbw.out, out)
     if err is not None:
       self.assertEqual(mbw.err, err)
     return mbw
 
   def test_clobber(self):
     files = {
@@ skipping 217 matching lines @@
     orig_stdout = sys.stdout
     try:
       sys.stdout = StringIO.StringIO()
       self.assertRaises(SystemExit, self.check, ['-h'])
       self.assertRaises(SystemExit, self.check, ['help'])
       self.assertRaises(SystemExit, self.check, ['help', 'gen'])
     finally:
       sys.stdout = orig_stdout
 
   def test_validate(self):
-    self.check(['validate'], ret=0)
+    mbw = self.fake_mbw()
+    mbw.files[mbw.default_config] = TEST_CONFIG
+    self.check(['validate'], mbw=mbw, ret=0)
 
   def test_bad_validate(self):
     mbw = self.fake_mbw()
     mbw.files[mbw.default_config] = TEST_BAD_CONFIG
-    self.check(['validate'], mbw=mbw, exception=TEST_BAD_CONFIG_ERR)
+    self.check(['validate'], mbw=mbw, ret=1)
 
 
 if __name__ == '__main__':
   unittest.main()