Add cleanup for measurements that use tracing

tools/perf/measurements/loading_trace_unittest.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 from measurements import loading_trace
 from telemetry.core import wpr_modes
 from telemetry.page import page_measurement_unittest_base
 from telemetry.unittest import options_for_unittests
 
 class LoadingTraceUnitTest(
       page_measurement_unittest_base.PageMeasurementUnitTestBase):
   def setUp(self):
     self._options = options_for_unittests.GetCopy()
     self._options.browser_options.wpr_mode = wpr_modes.WPR_OFF
 
   def testLoadingTraceBasic(self):
     ps = self.CreatePageSetFromFileInUnittestDataDir('scrollable_page.html')
     measurement = loading_trace.LoadingTrace()
     trace_options = self._options
     results = self.RunMeasurement(measurement, ps, options = trace_options)
     self.assertEquals(0, len(results.failures))
+
+  def testCleanUpTrace(self):
+    self.TestTracingCleanedUp(loading_trace.LoadingTrace, self._options)