[Systrace] Fix systrace clock syncing issue with BattOr.

systrace/systrace/tracing_agents/battor_trace_agent_unittest.py

Index: systrace/systrace/tracing_agents/battor_trace_agent_unittest.py
diff --git a/systrace/systrace/tracing_agents/battor_trace_agent_unittest.py b/systrace/systrace/tracing_agents/battor_trace_agent_unittest.py
index 5ef2a3faac04d85288473a9770db923e59edbba4..484e0bd69800458d3e073ca67e5041c41b53a192 100755
--- a/systrace/systrace/tracing_agents/battor_trace_agent_unittest.py
+++ b/systrace/systrace/tracing_agents/battor_trace_agent_unittest.py
@@ -13,6 +13,7 @@ from systrace.tracing_agents import battor_trace_agent
 from battor import battor_wrapper
 from devil.android import battery_utils
 from devil.utils import battor_device_mapping
+from devil.utils import find_usb_devices
 
 
 mock_opts = namedtuple('mock_opts', ['target', 'device_serial_number',
@@ -39,7 +40,8 @@ def setup_battor_test(StartShell_error, StartTracing_error,
     del kwargs
     return wrapper
   battor_wrapper.BattOrWrapper = wrapper_maker
-
+  find_usb_devices.GetBusNumberToDeviceTreeMap = lambda: None
+  battor_device_mapping.GetBattOrList = lambda x: ['/dev/ttyUSB0']
 
 class MockBattOrWrapper(object):
   def __init__(self, StartShell_error=False, StartTracing_error=False,