Rewrite the Android implementation of BatteryMonitor directly in Java.

device/battery/android/java/src/org/chromium/device/battery/BatteryMonitorFactory.java

Index: device/battery/android/java/src/org/chromium/device/battery/BatteryMonitorFactory.java
diff --git a/device/battery/android/java/src/org/chromium/device/battery/BatteryMonitorFactory.java b/device/battery/android/java/src/org/chromium/device/battery/BatteryMonitorFactory.java
new file mode 100644
index 0000000000000000000000000000000000000000..19498eff55e00b53d787c599cc8eb85a15a6070d
--- /dev/null
+++ b/device/battery/android/java/src/org/chromium/device/battery/BatteryMonitorFactory.java
@@ -0,0 +1,71 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.device.battery;
+
+import android.content.Context;
+import android.util.Log;
+
+import org.chromium.base.ApplicationStatus;
+import org.chromium.base.ThreadUtils;
+import org.chromium.device.battery.BatteryStatusManager.BatteryStatusCallback;
+import org.chromium.mojom.device.BatteryMonitor;
+import org.chromium.mojom.device.BatteryStatus;
+
+import java.util.HashSet;
+
+/**
+ * Factory that creates instances of BatteryMonitor implementations and notifies them about battery
+ * status changes.
+ */
+public class BatteryMonitorFactory {
+    static final String TAG = "BatteryMonitorFactory";
+
+    // Backing source of battery information.
+    private final BatteryStatusManager mManager;
+    // Monitors currently interested in the battery status notifications.
+    private final HashSet<BatteryMonitorImpl> mSubscribedMonitors =
+            new HashSet<BatteryMonitorImpl>();
+
+    private final BatteryStatusCallback mCallback = new BatteryStatusCallback() {
+        @Override
+        public void onBatteryStatusChanged(BatteryStatus batteryStatus) {
+            ThreadUtils.assertOnUiThread();
+
+            for (BatteryMonitorImpl monitor : mSubscribedMonitors) {
+                monitor.didChange(batteryStatus);
+            }
+        }
+    };
+
+    public BatteryMonitorFactory() {
+        Context applicationContext = ApplicationStatus.getApplicationContext();
+        assert applicationContext != null;
+        mManager = new BatteryStatusManager(applicationContext, mCallback);
+    }
+
+    public BatteryMonitor createMonitor() {
+        ThreadUtils.assertOnUiThread();
+
+        if (mSubscribedMonitors.isEmpty() && !mManager.start()) {
+            Log.e(TAG, "BatteryStatusManager failed to start.");
+        }
+        // TODO(ppi): record the "BatteryStatus.StartAndroid" histogram here once we have a Java API
+        //            for UMA - http://crbug.com/442300.
+
+        BatteryMonitorImpl monitor = new BatteryMonitorImpl(this);
+        mSubscribedMonitors.add(monitor);
+        return monitor;
+    }
+
+    void unsubscribe(BatteryMonitorImpl monitor) {
+        ThreadUtils.assertOnUiThread();
+
+        assert mSubscribedMonitors.contains(monitor);
+        mSubscribedMonitors.remove(monitor);
+        if (mSubscribedMonitors.isEmpty()) {
+            mManager.stop();
+        }
+    }
+}