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..5c5cf732a0a1bf4021072bdb59e538323dcdde5c
--- /dev/null
+++ b/build/android/pylib/device/device_list.py
@@ -0,0 +1,36 @@
+# 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."""

[jbudorick, 2014/06/03 13:52:52]

I'm not sure that this module goes far enough - it'd be nice to have the
persistent device list logic more self-contained - but for now, it's ok.
Something to think about down the line, though.

+
+import os
+
+LAST_DEVICES_FILENAME = '.last_devices'
+LAST_MISSING_DEVICES_FILENAME = '.last_missing'
+
+
+def GetDeviceList(file_name):

[jbudorick, 2014/06/03 13:52:52]

This should be renamed to avoid confusion with AdbWrapper.GetDevices /
android_commands.GetAttachedDevices. GetPersistentDeviceList, GetLastDevices,
...? Something that indicates that the list of devices being retrieved is not a
list of the currently attached devices.

[bulach, 2014/06/03 14:25:52]

good point! Get|WritePersistentDeviceList.

+  """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.
+  """
+  devices = []
+  try:
+    with open(file_name) as f:
+      devices = f.read().splitlines()
+  except IOError:
+    # Ignore error, file might not exist
+    pass

[jbudorick, 2014/06/03 13:52:52]

This should log something. Not an error, obviously, but maybe a warning.

[bulach, 2014/06/03 14:25:52]

good catch.. the exception shouldn't be handled here, but rather by the callers.

+  return devices
+
+
+def WriteDeviceList(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)))