Make TrialDirMixIn so it can be used stand alone.

This will be used in commit queue tests.

R=dpranke@chromium.org
BUG=
TEST=

Review URL: http://codereview.chromium.org/7046110

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@88986 0039d316-1c4b-4281-b951-d872f2087c98

tests/trial_dir.py

@@ -65,8 +65,7 @@ class TrialDir(object):
       logging.error('Leaking %s' % TrialDir.TRIAL_ROOT)
 
 
-class TestCase(unittest.TestCase):
-  """Base unittest class that cleans off a trial directory in tearDown()."""
+class TrialDirMixIn(object):
   def setUp(self):
     # Create a specific directory just for the test.
     self.trial = TrialDir(self.id())
@@ -80,6 +79,17 @@ class TestCase(unittest.TestCase):
     return self.trial.root_dir
 
 
+class TestCase(unittest.TestCase, TrialDirMixIn):
+  """Base unittest class that cleans off a trial directory in tearDown()."""
+  def setUp(self):
+    unittest.TestCase.setUp(self)
+    TrialDirMixIn.setUp(self)
+
+  def tearDown(self):
+    TrialDirMixIn.tearDown(self)
+    unittest.TestCase.tearDown(self)
+
+
 if '-l' in sys.argv:
   # See SHOULD_LEAK definition in TrialDir for its purpose.
   TrialDir.SHOULD_LEAK = True