batteryservice: Add battery capacity

Change-Id: I6879ec9ec931cbea82aa550b3b227e744255bfd4
diff --git a/include/batteryservice/BatteryService.h b/include/batteryservice/BatteryService.h
index 7ae1342..2902d17 100644
--- a/include/batteryservice/BatteryService.h
+++ b/include/batteryservice/BatteryService.h
@@ -48,6 +48,7 @@
     BATTERY_PROP_CHARGE_COUNTER = 1, // equals BatteryProperty.BATTERY_PROP_CHARGE_COUNTER constant
     BATTERY_PROP_CURRENT_NOW = 2, // equals BatteryProperty.BATTERY_PROP_CURRENT_NOW constant
     BATTERY_PROP_CURRENT_AVG = 3, // equals BatteryProperty.BATTERY_PROP_CURRENT_AVG constant
+    BATTERY_PROP_CAPACITY = 4, // equals BatteryProperty.BATTERY_PROP_CAPACITY constant
 };
 
 struct BatteryProperties {