[telemetry] Create BrowserTestCase to reuse the browser for browser_unittest.

tools/perf/measurements/thread_times_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 thread_times
 from measurements import smoothness_unittest
 from metrics import timeline
 from telemetry.core import wpr_modes
-from telemetry.testing import page_test_test_case
 from telemetry.unittest import options_for_unittests
+from telemetry.unittest import page_test_test_case
 from telemetry.unittest import test
 
 
 
 class ThreadTimesUnitTest(page_test_test_case.PageTestTestCase):
   def setUp(self):
     self._options = options_for_unittests.GetCopy()
     self._options.browser_options.wpr_mode = wpr_modes.WPR_OFF
 
   @test.Disabled('android')
@@ skipping 19 matching lines @@
     self.assertEquals(0, len(results.failures))
 
     for category in timeline.TimelineThreadCategories.values():
       cpu_time_name = timeline.ThreadCpuTimeResultName(category)
       cpu_time = results.FindAllPageSpecificValuesNamed(cpu_time_name)
       self.assertEquals(len(cpu_time), 1)
 
 
   def testCleanUpTrace(self):
     self.TestTracingCleanedUp(thread_times.ThreadTimes, self._options)