[Android] Change battery_utils TieredSetCharging from exceptions based to discovery based

build/android/pylib/device/battery_utils.py

 # Copyright 2015 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.
 
 """Provides a variety of device interactions with power.
 """
 # pylint: disable=unused-argument
 
 import collections
 import contextlib
@@ skipping 469 matching lines @@
     Args:
       enabled: A boolean indicating whether charging should be enabled or
         disabled.
       timeout: timeout in seconds
       retries: number of retries
     """
     if self.GetCharging() == enabled:
       logging.warning('Device charging already in expected state: %s', enabled)
       return
 
+    self._DiscoverDeviceProfile()
     if enabled:
-      try:
+      if self._cache['profile']['enable_command']:
         self.SetCharging(enabled)
-      except device_errors.CommandFailedError:
-        logging.info('Unable to enable charging via hardware.'
-                     ' Falling back to software enabling.')
+      else:

[perezju, 2015/08/18 09:14:15]

nit: maybe keep a logging.info to indicate whether we're doing hardware/software
enable/disable?

[rnephew (Wrong account), 2015/08/18 14:54:53]

Done.

         self.EnableBatteryUpdates()
     else:
-      try:
+      if self._cache['profile']['enable_command']:
         self._ClearPowerData()
         self.SetCharging(enabled)
-      except device_errors.CommandFailedError:
-        logging.info('Unable to disable charging via hardware.'
-                     ' Falling back to software disabling.')
+      else:
         self.DisableBatteryUpdates()
 
   @contextlib.contextmanager
   def PowerMeasurement(self, timeout=None, retries=None):
     """Context manager that enables battery power collection.
 
     Once the with block is exited, charging is resumed. Will attempt to disable
     charging at the hardware level, and if that fails will fall back to software
     disabling of battery updates.
 
@@ skipping 71 matching lines @@
     self._cache['profile'] = {
         'name': None,
         'witness_file': None,
         'enable_command': None,
         'disable_command': None,
         'charge_counter': None,
         'voltage': None,
         'current': None,
     }
     return False