Wrap "import pexpect" in a try-expect.

build/android/pylib/android_commands.py

 # Copyright (c) 2012 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.
 
 """Provides an interface to communicate with the device via the adb command.
 
 Assumes adb binary is currently on system path.
 """
 
 import collections
 import datetime
 import logging
 import os
 import re
 import shlex
 import subprocess
 import sys
 import tempfile
 import time
 
 import io_stats_parser
-import pexpect
+try:
+  import pexpect
+except:
+  pexpect = None
 
 CHROME_SRC = os.path.join(
     os.path.abspath(os.path.dirname(__file__)), '..', '..', '..')
 
 sys.path.append(os.path.join(CHROME_SRC, 'third_party', 'android_testrunner'))
 import adb_interface
 
 import cmd_helper
 import errors  #  is under ../../../third_party/android_testrunner/errors.py
 
@@ skipping 1028 matching lines @@
   def __init__(self, output):
     self._output = output
 
   def write(self, data):
     data = data.replace('\r\r\n', '\n')
     self._output.write(data)
 
   def flush(self):
     self._output.flush()