add API to query battery status on Android

frontend/ui/device.lua

@@ -1,3 +1,4 @@
+local AndroidPowerd = require("ui/device/androidpowerd")
 local KindlePowerD = require("ui/device/kindlepowerd")
 local KoboPowerD = require("ui/device/kobopowerd")
 local BasePowerD = require("ui/device/basepowerd")
@@ -259,6 +260,8 @@ function Device:getPowerDevice()
             self.powerd = KindlePowerD:new{model = model}
         elseif self:isKobo() then
             self.powerd = KoboPowerD:new()
+        elseif self.isAndroid then
+            self.powerd = AndroidPowerd:new()
         else -- emulated FrontLight
             self.powerd = BasePowerD:new()
         end

frontend/ui/device/androidpowerd.lua

@@ -0,0 +1,26 @@
+local BasePowerD = require("ui/device/basepowerd")
+
+local AndroidPowerD = BasePowerD:new{
+    batt_capacity_file = "/sys/class/power_supply/battery/capacity",
+    is_charging_file = "/sys/class/power_supply/battery/charging_enabled",
+    battCapacity = nil,
+    is_charging = nil,
+}
+
+function AndroidPowerD:init()
+end
+
+function AndroidPowerD:setIntensityHW()
+end
+
+function AndroidPowerD:getCapacityHW()
+    self.battCapacity = self:read_int_file(self.batt_capacity_file)
+    return self.battCapacity
+end
+
+function AndroidPowerD:isChargingHW()
+    self.is_charging = self:read_int_file(self.is_charging_file)
+    return self.is_charging == 1
+end
+
+return AndroidPowerD