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

build/android/pylib/device/battery_utils.py

Index: build/android/pylib/device/battery_utils.py
diff --git a/build/android/pylib/device/battery_utils.py b/build/android/pylib/device/battery_utils.py
index ac5e7a87ae9187709b1d16f0f18bd6bb78dda183..858f7c5be2d3ac196fbd54afafd34d26539ae995 100644
--- a/build/android/pylib/device/battery_utils.py
+++ b/build/android/pylib/device/battery_utils.py
@@ -487,20 +487,17 @@ class BatteryUtils(object):
       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