Adding battery control API for android.

build/android/pylib/android_commands.py

Index: build/android/pylib/android_commands.py
diff --git a/build/android/pylib/android_commands.py b/build/android/pylib/android_commands.py
index f000682b70641709bfe193dc6e13ebded47424c8..d0fc6c9f2003ada8f79d1346d18786c02127a644 100644
--- a/build/android/pylib/android_commands.py
+++ b/build/android/pylib/android_commands.py
@@ -73,6 +73,15 @@ MD5SUM_DEVICE_FOLDER = constants.TEST_EXECUTABLE_DIR + '/md5sum/'
 MD5SUM_DEVICE_PATH = MD5SUM_DEVICE_FOLDER + 'md5sum_bin'
 MD5SUM_LD_LIBRARY_PATH = 'LD_LIBRARY_PATH=%s' % MD5SUM_DEVICE_FOLDER
 
+CONTROL_USB_CHARGING_COMMANDS = [
+  {
+    # Nexus 4
+    'witness_file': '/sys/module/pm8921_charger/parameters/disabled',
+    'enable_command': 'echo 0 > /sys/module/pm8921_charger/parameters/disabled',
+    'disable_command':
+        'echo 1 > /sys/module/pm8921_charger/parameters/disabled',
+  },
+]
 
 def GetAVDs():
   """Returns a list of AVDs."""
@@ -285,6 +294,10 @@ class AndroidCommands(object):
     self._util_wrapper = ''
     self._system_properties = system_properties.SystemProperties(self.Adb())
     self._push_if_needed_cache = {}
+    self._control_usb_charging_command = {
+        'command': None,
+        'cached': False,
+    }
 
   @property
   def system_properties(self):
@@ -1825,6 +1838,38 @@ class AndroidCommands(object):
       logging.info('[%s]> %s', device_repr, line)
     self.RunShellCommand('rm %s' % temp_script_file)
 
+  def _GetControlUsbChargingCommand(self):
+    if self._control_usb_charging_command['cached']:
+      return self._control_usb_charging_command['command']
+    self._control_usb_charging_command['cached'] = True
+    for command in CONTROL_USB_CHARGING_COMMANDS:
+      # Assert command is valid.
+      assert 'disable_command' in command
+      assert 'enable_command' in command
+      assert 'witness_file' in command
+      witness_file = command['witness_file']
+      if self.FileExistsOnDevice(witness_file):
+        self._control_usb_charging_command['command'] = command
+        return command
+    return None
+
+  def CanControlUsbCharging(self):
+    return self._GetControlUsbChargingCommand() is not None
+
+  def DisableUsbCharging(self):
+    command = self._GetControlUsbChargingCommand()
+    if not command:
+      raise Exception('Unable to act on usb charging.')
+    disable_command = command['disable_command']
+    self.RunShellCommand(disable_command)
+
+  def EnableUsbCharging(self):
+    command = self._GetControlUsbChargingCommand()
+    if not command:
+      raise Exception('Unable to act on usb charging.')
+    disable_command = command['enable_command']
+    self.RunShellCommand(disable_command)
+
 
 class NewLineNormalizer(object):
   """A file-like object to normalize EOLs to '\n'.