android: Fix importing pexpect on Mac

build/android/pylib/perf/test_runner.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.
 
 """Runs a perf test on a single device.
 
 Our buildbot infrastructure requires each slave to run steps serially.
 This is sub-optimal for android, where these steps can run independently on
 multiple connected devices.
 
@@ skipping 27 matching lines @@
 
 Note that script_to_execute necessarily have to take at least the following
 options:
   --device: the serial number to be passed to all adb commands.
   --keep_test_server_ports: indicates it's being run as a shard, and shouldn't
   reset test server port allocation.
 """
 
 import datetime
 import logging
-import pexpect
 import pickle
 import os
 import sys
 
 from pylib import constants
+from pylib import pexpect
 from pylib.base import base_test_result
 from pylib.base import base_test_runner
 
 
 def PrintTestOutput(test_name):
   """Helper method to print the output of previously executed test_name.
 
   Args:
     test_name: name of the test that has been previously executed.
 
@@ skipping 100 matching lines @@
     Returns:
       A tuple of (TestRunResults, retry).
     """
     output, result_type = self._LaunchPerfTest(test_name)
     results = base_test_result.TestRunResults()
     results.AddResult(base_test_result.BaseTestResult(test_name, result_type))
     retry = None
     if not results.DidRunPass():
       retry = test_name
     return results, retry