[Android] Introduce RegistrationPolicy for NetworkChangeNotifier.

net/android/java/src/org/chromium/net/RegistrationPolicyAlwaysRegister.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;
+
+/**
+ * Registration policy which make sure that the listener is always registered.
+ */
+public class RegistrationPolicyAlwaysRegister
+        extends NetworkChangeNotifierAutoDetect.RegistrationPolicy {
+    @Override
+    protected void init(NetworkChangeNotifierAutoDetect notifier) {
+        super.init(notifier);
+        register();
+    }
+
+    protected void destroy() {}
+}