Adding battery status updates for new observers for Android

This CL adds parity between Android and Desktop for new battery
monitors. Currently, the second observer that is added for battery will
only receive new updates. This cl pushes the latest battery status
update to the new observer.

Bug: 999063
Change-Id: I6cfa7eeb6a355d03f2b1f0d9e8b7a73ffd8452e3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1829023Reviewed-by: Colin Blundell <blundell@chromium.org>
Commit-Queue: Ryan Sturm <ryansturm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#700827}

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

@@ -27,12 +27,18 @@ public class BatteryMonitorFactory implements InterfaceFactory<BatteryMonitor> {
     // Monitors currently interested in the battery status notifications.
     private final HashSet<BatteryMonitorImpl> mSubscribedMonitors =
             new HashSet<BatteryMonitorImpl>();
+    // Tracks the latest battery status update for newly added observers.
+    private boolean mHasStatusUpdate;
+    private BatteryStatus mBatteryStatus;
 
     private final BatteryStatusCallback mCallback = new BatteryStatusCallback() {
         @Override
         public void onBatteryStatusChanged(BatteryStatus batteryStatus) {
             ThreadUtils.assertOnUiThread();
 
+            mHasStatusUpdate = true;
+            mBatteryStatus = batteryStatus;
+
             List<BatteryMonitorImpl> monitors = new ArrayList<>(mSubscribedMonitors);
             for (BatteryMonitorImpl monitor : monitors) {
                 monitor.didChange(batteryStatus);
@@ -41,6 +47,7 @@ public class BatteryMonitorFactory implements InterfaceFactory<BatteryMonitor> {
     };
 
     public BatteryMonitorFactory() {
+        mHasStatusUpdate = false;
         mManager = new BatteryStatusManager(mCallback);
     }
 
@@ -55,6 +62,10 @@ public class BatteryMonitorFactory implements InterfaceFactory<BatteryMonitor> {
         //            for UMA - http://crbug.com/442300.
 
         BatteryMonitorImpl monitor = new BatteryMonitorImpl(this);
+        if (mHasStatusUpdate) {
+            monitor.didChange(mBatteryStatus);
+        }
+
         mSubscribedMonitors.add(monitor);
         return monitor;
     }
@@ -66,6 +77,7 @@ public class BatteryMonitorFactory implements InterfaceFactory<BatteryMonitor> {
         mSubscribedMonitors.remove(monitor);
         if (mSubscribedMonitors.isEmpty()) {
             mManager.stop();
+            mHasStatusUpdate = false;
         }
     }
 }