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..c717e931958bb6954b807c1288fe2d1edf8ffef6 100644
--- a/build/android/pylib/device/device_utils.py
+++ b/build/android/pylib/device/device_utils.py
@@ -69,6 +69,11 @@ _CONTROL_CHARGING_COMMANDS = [
   },
 ]
 
+_DEFAULT_CHARGING_COMMANDS = {
+    'witness_file': None,
+    'enable_command': 'dumpsys battery reset',
+    'disable_command': 'dumpsys battery set usb 0',
+}
 
 @decorators.WithExplicitTimeoutAndRetries(
     _DEFAULT_TIMEOUT, _DEFAULT_RETRIES)
@@ -1414,8 +1419,10 @@ 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 ':' in line:
+        k, v = line.split(': ', 1)
+        result[k.strip()] = v.strip()

[perezju, 2015/03/10 09:46:09]

I think you should just log a warning on all skipped lines.

     return result
 
   @decorators.WithTimeoutAndRetriesFromInstance()
@@ -1451,8 +1458,9 @@ class DeviceUtils(object):
           self._cache['charging_config'] = c
           break
       else:
-        raise device_errors.CommandFailedError(
-            'Unable to find charging commands.')
+        logging.warning('No charging information found.'
+                        'Defaulting to generic values.')
+        self._cache['charging_config'] = _DEFAULT_CHARGING_COMMANDS

[jbudorick, 2015/03/10 00:04:43]

This isn't quite what I suggested in the last CL. I think we should do _both_
the default command _and_ the specific commands on N4 and N5, and just do the
default command otherwise. This _only_ does the default command if there's no
specific command.

[perezju, 2015/03/10 09:46:09]

I'm not entirely sure I understand what these dumpsys enable/disable commands
are supposed to do, or how do we plan to use them.

From what I can gather, "set usb 0" will "freeze" the values reported by
GetBatteryInfo until we do a "reset". Is that right?

Why would we want to do this every time we disable charging? Wouldn't we usually
want to disable charging but expect GetBatteryInfo to keep returning accurate
values regarding, e.g., current charge levels?

[jbudorick, 2015/03/10 13:22:35]

AFAIK this actually affects charging to some degree as well (maybe only on
specific OS versions, in which case we should tune this to those). rnephew may
be able to explain in more detail...

 
     if enabled:
       command = self._cache['charging_config']['enable_command']