[devil] Detect if device is not charging properly.

devil/devil/android/device_errors.py

Index: devil/devil/android/device_errors.py
diff --git a/devil/devil/android/device_errors.py b/devil/devil/android/device_errors.py
index ea14bf9ad8b9a7d144ce70fc4cd3559b0541c7b7..b1b8890f45105d6d2755bece46a80715677e0389 100644
--- a/devil/devil/android/device_errors.py
+++ b/devil/devil/android/device_errors.py
@@ -115,3 +115,10 @@ class NoAdbError(base_error.BaseError):
   def __init__(self, msg=None):
     super(NoAdbError, self).__init__(
         msg or 'Unable to find adb.', is_infra_error=True)
+
+
+class DeviceChargingError(CommandFailedError):
+  """Exception for device charging errors."""
+
+  def __init__(self, message, device_serial=None):
+    super(DeviceChargingError, self).__init__(message, device_serial)