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

tools/perf/measurements/rasterize_and_record_micro_unittest.py

 # Copyright 2013 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.
 
 import logging
 
 from measurements import rasterize_and_record_micro
 from telemetry.core import wpr_modes
 from telemetry.page import page_test
-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
-from telemetry.unittest import options_for_unittests
 
 
 class RasterizeAndRecordMicroUnitTest(page_test_test_case.PageTestTestCase):
   """Smoke test for rasterize_and_record_micro measurement
 
      Runs rasterize_and_record_micro measurement on a simple page and verifies
      that all metrics were added to the results. The test is purely functional,
      i.e. it only checks if the metrics are present and non-zero.
   """
 
@@ skipping 63 matching lines @@
         total_picture_layers_with_no_content[0].GetRepresentativeNumber(), 0)
 
     total_picture_layers_off_screen = \
         results.FindAllPageSpecificValuesNamed(
             'total_picture_layers_off_screen')
     self.assertEquals(len(total_picture_layers_off_screen), 1)
     self.assertEqual(
         total_picture_layers_off_screen[0].GetRepresentativeNumber(), 0)