Android: adds device affinity for perf tests.

build/android/pylib/device/device_list.py

Index: build/android/pylib/device/device_list.py
diff --git a/build/android/pylib/device/device_list.py b/build/android/pylib/device/device_list.py
new file mode 100644
index 0000000000000000000000000000000000000000..0eb6acba2b28b66c0c473f6ecd615f70f39f73b9
--- /dev/null
+++ b/build/android/pylib/device/device_list.py
@@ -0,0 +1,30 @@
+# 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.
+
+"""A module to keep track of devices across builds."""
+
+import os
+
+LAST_DEVICES_FILENAME = '.last_devices'
+LAST_MISSING_DEVICES_FILENAME = '.last_missing'
+
+
+def GetPersistentDeviceList(file_name):
+  """Returns a list of devices.
+
+  Args:
+    file_name: the file name containing a list of devices.
+
+  Returns: List of device serial numbers that were on the bot.
+  """
+  with open(file_name) as f:
+    return f.read().splitlines()
+
+
+def WritePersistentDeviceList(file_name, device_list):
+  path = os.path.dirname(file_name)
+  if not os.path.exists(path):
+    os.makedirs(path)
+  with open(file_name, 'w') as f:
+    f.write('\n'.join(set(device_list)))