Fix small error in SimpleMock.

It's bad python practice to use a class-level member that is mutable. self.calls
is already initialized in __init__ so it's not useful (and dangerous) to have it
as a class member.

R=cmp@chromium.org
BUG=


Review URL: https://chromiumcodereview.appspot.com/11801018

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@175368 0039d316-1c4b-4281-b951-d872f2087c98

testing_support/auto_stub.py

@@ -56,8 +56,6 @@ class AutoStubMixIn(object):
 
 class SimpleMock(object):
   """Really simple manual class mock."""
-  calls = []
-
   def __init__(self, unit_test):
     """Do not call __init__ if you want to use the global call list to detect
     ordering across different instances.