[autotest] Add test for the re-taking of ownership after the owner key is lost

client/site_tests/login_OwnershipTaken/login_OwnershipTaken.py

Index: client/site_tests/login_OwnershipTaken/login_OwnershipTaken.py
diff --git a/client/site_tests/login_OwnershipTaken/login_OwnershipTaken.py b/client/site_tests/login_OwnershipTaken/login_OwnershipTaken.py
index 2eb79d5f0a91179c073a72efd53a701471b2e8b1..533cffeb8f3143f9088de613411418ca6d81505c 100644
--- a/client/site_tests/login_OwnershipTaken/login_OwnershipTaken.py
+++ b/client/site_tests/login_OwnershipTaken/login_OwnershipTaken.py
@@ -33,33 +33,7 @@ class login_OwnershipTaken(cros_ui_test.UITest):
         login.wait_for_ownership()
 
         sm = ownership.connect_to_session_manager()
-
         retrieved_policy = sm.RetrievePolicy(byte_arrays=True)
         if retrieved_policy is None:
             raise error.TestFail('Policy not found')
-
-        # Pull in protobuf definitions.
-        sys.path.append(self.srcdir)
-        from device_management_backend_pb2 import PolicyFetchResponse
-        from device_management_backend_pb2 import PolicyData
-        from chrome_device_policy_pb2 import ChromeDeviceSettingsProto
-        from chrome_device_policy_pb2 import UserWhitelistProto
-
-        policy_proto = PolicyFetchResponse()
-        policy_proto.ParseFromString(retrieved_policy)
-        poldata = PolicyData()
-        poldata.ParseFromString(policy_proto.policy_data)
-        if (not poldata.HasField('username') or
-            poldata.username != self.username):
-            raise error.TestFail('Username not appropriately set in policy')
-
-        polval = ChromeDeviceSettingsProto()
-        polval.ParseFromString(poldata.policy_value)
-        if (not polval.HasField('allow_new_users') or
-            not polval.allow_new_users.HasField('allow_new_users') or
-            not polval.allow_new_users):
-            raise error.TestFail('Whitelisting not disabled in policy')
-
-        if (not polval.HasField('user_whitelist') or
-            not self.username in polval.user_whitelist.user_whitelist):
-            raise error.TestFail('Owner not whitelisted')
+        self.validate_basic_policy(retrieved_policy)