Add new method to disable android device charging.

build/android/pylib/device/device_utils.py

Index: build/android/pylib/device/device_utils.py
diff --git a/build/android/pylib/device/device_utils.py b/build/android/pylib/device/device_utils.py
index b6fd7323bb9a3c71e566049719a963bba2ce9023..1265cce765ce81713bcb9da5b85306926e84ef7c 100644
--- a/build/android/pylib/device/device_utils.py
+++ b/build/android/pylib/device/device_utils.py
@@ -9,6 +9,7 @@ Eventually, this will be based on adb_wrapper.
 # pylint: disable=unused-argument
 
 import collections
+import contextlib
 import itertools
 import logging
 import multiprocessing
@@ -69,7 +70,6 @@ _CONTROL_CHARGING_COMMANDS = [
   },
 ]
 
-

[perezju, 2015/03/17 12:52:19]

nit: this line went missing

 @decorators.WithExplicitTimeoutAndRetries(
     _DEFAULT_TIMEOUT, _DEFAULT_RETRIES)
 def GetAVDs():
@@ -1414,8 +1414,16 @@ class DeviceUtils(object):
     # Skip the first line, which is just a header.
     for line in self.RunShellCommand(
         ['dumpsys', 'battery'], check_return=True)[1:]:
-      k, v = line.split(': ', 1)
-      result[k.strip()] = v.strip()
+      # If usb charging has been disabled, an extra line of header exists.
+      if 'UPDATES STOPPED' in line:
+        logging.warning('Dumpsys battery not receiving updates. '
+                        'Run dumpsys battery reset if this is in error.')
+      elif ':' not in line:
+        logging.warning('Unknown line found in dumpsys battery.')
+        logging.warning(line)
+      else:
+        k, v = line.split(': ', 1)
+        result[k.strip()] = v.strip()
     return result
 
   @decorators.WithTimeoutAndRetriesFromInstance()
@@ -1466,6 +1474,57 @@ class DeviceUtils(object):
     timeout_retry.WaitFor(set_and_verify_charging, wait_period=1)
 
   @decorators.WithTimeoutAndRetriesFromInstance()
+  def _DisableBatteryUpdates(self, timeout=None, retries=None):
+    def battery_updates_disabled():
+      return self.GetCharging() is False
+
+    self.RunShellCommand(
+        ['dumpsys', 'batterystats', '--reset'], check_return=True)
+    battery_data = self.RunShellCommand(
+        ['dumpsys', 'batterystats', '--charged',
+        '--checkin'], check_return=True)
+    for line in battery_data:
+      l = line.split(',')
+      if l[3] == 'pwi' and l[1] != 0:
+        raise device_errors.CommandFailedError(
+            'Non-zero pmi value found after reset.')
+    self.RunShellCommand(['dumpsys', 'battery', 'set', 'usb', '0'],
+                         check_return=True)
+    timeout_retry.WaitFor(battery_updates_disabled, wait_period=1)
+
+  @decorators.WithTimeoutAndRetriesFromInstance()
+  def _EnableBatteryUpdates(self, timeout=None, retries=None):
+    def battery_updates_enabled():
+      return self.GetCharging() is True
+
+    self.RunShellCommand(['dumpsys', 'battery', 'reset'], check_return=True)
+    timeout_retry.WaitFor(battery_updates_enabled, wait_period=1)
+
+  @contextlib.contextmanager
+  def BatteryMeasurement(self, timeout=None, retries=None):
+    """Context manager that enables battery data collection when in.
+    Only for devices L and higher.
+
+    Example usage:
+      with BatteryMeasurement():
+        browser_actions()
+        get_power_data() # report usage within this block
+      after_measurements() # Anything that runs after power
+                           # measurements are collected

[perezju, 2015/03/17 12:52:19]

nit: I think these comments could be improved a bit. I understand that battery
measurements within the context manager block will report usage relative to the
start of the block ("as if" the device had stopped charging then); while battery
measurements taken after exiting the block will revert to report live usage (and
do not aggregate data that would otherwise be collected "since last charge").

Is this more or less accurate? Could you update the comments to better reflect
the intended behavior?

[rnephew (Wrong account), 2015/03/17 19:58:42]

Done.

+
+    Args:
+      timeout: timeout in seconds
+      retries: number of retries
+    """
+    if self.build_version_sdk < constants.ANDROID_SDK_VERSION_CODES.LOLLIPOP:
+      raise device_errors.CommandFailedError('Device must be L or higher.')
+    try:
+      self._DisableBatteryUpdates(timeout=timeout, retries=retries)
+      yield
+    finally:
+      self._EnableBatteryUpdates(timeout=timeout, retries=retries)
+
+  @decorators.WithTimeoutAndRetriesFromInstance()
   def GetDevicePieWrapper(self, timeout=None, retries=None):
     """Gets the absolute path to the run_pie wrapper on the device.