Rewrite the Android implementation of BatteryMonitor directly in Java.

device/battery/android/BUILD.gn

Index: device/battery/android/BUILD.gn
diff --git a/device/battery/android/BUILD.gn b/device/battery/android/BUILD.gn
index f88cfc0b3deee30d6e91850be43bee8cc5a8f7c6..ea4d5cc84bd146059049a58bdc9bbaa2b7de7ae3 100644
--- a/device/battery/android/BUILD.gn
+++ b/device/battery/android/BUILD.gn
@@ -5,9 +5,17 @@
 import("//build/config/android/config.gni")
 import("//build/config/android/rules.gni")
 
-generate_jni("battery_jni_headers") {
-  jni_package = "battery"
-  sources = [
+android_library("battery_monitor_android") {
+  java_files = [
     "java/src/org/chromium/device/battery/BatteryStatusManager.java",
+    "java/src/org/chromium/device/battery/BatteryMonitorImpl.java",
+    "java/src/org/chromium/device/battery/BatteryMonitorFactory.java",
+  ]
+
+  deps = [
+    "//base:base_java",
+    "//device/battery:mojo_bindings_java",
+    "//mojo/public/java:bindings",
+    "//mojo/public/java:system",
   ]
 }