[Android] Introduce RegistrationPolicy for NetworkChangeNotifier.

net/android/java/src/org/chromium/net/RegistrationPolicyApplicationStatus.java

+// Copyright 2015 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.net;
+
+import org.chromium.base.ApplicationState;
+import org.chromium.base.ApplicationStatus;
+import org.chromium.base.VisibleForTesting;
+
+/**
+ * Regsitration policy which depends on the ApplicationState.
+ */
+public class RegistrationPolicyApplicationStatus
+        extends RegistrationPolicy implements ApplicationStatus.ApplicationStateListener {
+    private boolean mDestroyed = false;
+
+    public RegistrationPolicyApplicationStatus() {}

[pauljensen, 2015/10/01 12:06:37]

why do we need a constructor?

[timvolodine, 2015/10/05 17:26:45]

no need, done.

+
+    protected void init(Listener listener) {
+        super.init(listener);
+        onApplicationStateChange(getApplicationState());
+        ApplicationStatus.registerApplicationStateListener(this);
+    }
+
+    protected void destroy() {
+        if (mDestroyed) return;
+        ApplicationStatus.unregisterApplicationStateListener(this);
+        mDestroyed = true;
+    }
+
+    // ApplicationStatus.ApplicationStateListener
+    @Override
+    public void onApplicationStateChange(int newState) {
+        if (newState == ApplicationState.HAS_RUNNING_ACTIVITIES) {
+            notifyRegister();
+        } else if (newState == ApplicationState.HAS_PAUSED_ACTIVITIES) {
+            notifyUnregister();
+        }
+    }
+
+    /**
+     * Returns the activity's status.
+     * @return an {@code int} that is one of {@code ApplicationState.HAS_*_ACTIVITIES}.
+     */
+    @VisibleForTesting
+    int getApplicationState() {
+        return ApplicationStatus.getStateForApplication();
+    }
+}