Add master.cfg unittest to help migration - pass BuildStep instances instead of BuildStep subclasses
https://bugs.webkit.org/show_bug.cgi?id=89564

Reviewed by Tony Chang.

* BuildSlaveSupport/build.webkit.org-config/mastercfg_unittest.py:
(BuildStepsConstructorTest):
(BuildStepsConstructorTest.generateTests):
(BuildStepsConstructorTest.createTest):
(BuildStepsConstructorTest.createTest.doTest):

git-svn-id: svn://svn.chromium.org/blink/trunk@121328 bbb929c8-8fbe-4397-9dbb-9b2b20218538