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

tools/perf/measurements/repaint_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 repaint
 from telemetry.core import wpr_modes
 from telemetry.page import page as page_module
-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 TestRepaintPage(page_module.Page):
   def __init__(self, page_set, base_dir):
     super(TestRepaintPage, self).__init__('file://blank.html',
                                           page_set, base_dir)
 
   def RunRepaint(self, action_runner):
     action_runner.RepaintContinuously(seconds=2)
@@ skipping 30 matching lines @@
     self.assertEquals(len(jank), 1)
     self.assertGreater(jank[0].GetRepresentativeNumber(), 0)
 
     mostly_smooth = results.FindAllPageSpecificValuesNamed('mostly_smooth')
     self.assertEquals(len(mostly_smooth), 1)
     self.assertGreaterEqual(mostly_smooth[0].GetRepresentativeNumber(), 0)
 
   @test.Disabled('android')
   def testCleanUpTrace(self):
     self.TestTracingCleanedUp(repaint.Repaint, self._options)