[Android] Add a configurable environment for devil/.

build/android/devil/android/logcat_monitor_test.py

Index: build/android/devil/android/logcat_monitor_test.py
diff --git a/build/android/devil/android/logcat_monitor_test.py b/build/android/devil/android/logcat_monitor_test.py
index 2b7969c4e745cae26f859ac75672082f656c3650..0123fe170500a95ba85b99658b63952f9b8179b1 100755
--- a/build/android/devil/android/logcat_monitor_test.py
+++ b/build/android/devil/android/logcat_monitor_test.py
@@ -6,16 +6,14 @@
 # pylint: disable=protected-access
 
 import itertools
-import os
 import sys
 import unittest
 
+from devil import env
 from devil.android import logcat_monitor
 from devil.android.sdk import adb_wrapper
-from pylib import constants
 
-sys.path.append(os.path.join(
-    constants.DIR_SOURCE_ROOT, 'third_party', 'pymock'))
+sys.path.append(env.dependencies.pymock_path)
 import mock # pylint: disable=F0401