[Android] Introduce RegistrationPolicy for NetworkChangeNotifier.

net/android/java/src/org/chromium/net/RegistrationPolicy.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;
+
+/**
+ * Abstract class for providing a policy regarding when the NetworkChangeNotifier
+ * should listen for network changes.
+ */
+public abstract class RegistrationPolicy {

[pauljensen, 2015/10/01 12:06:36]

Can we move this to be a static subclass of NetworkChangeNotifier (NCN)?  I
think this makes the class's scope more clearly match what this class is used
for.  Then we could remove the Listener class which I find confusing, replace
mListener with a NCN pointer, and just have RegistrationPolicy.notifyRegister()
call private NCN functions directly.

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

made it inner static to NCNAD and removed the Listener interface.

+    private Listener mListener;
+
+    /**
+     * Listener is notified by the policy when it should start/stop listening to network changes.
+     */
+    public interface Listener {
+        // Notifies the listener to start listening to network changes.
+        void register();
+        // Notifies the listener tp stop listening to network changes.
+        void unregister();
+    }
+
+    protected RegistrationPolicy() {}

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

why do we need a constructor?

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

yup no need, removed. done.

+
+    protected final void notifyRegister() {

[pauljensen, 2015/10/01 12:06:36]

Can we rename notifyRegister to register? ditto for notifyUnregister

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

Please add a comments for these functions; they represent an API.

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

Done.

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

Done.

+        assert mListener != null;
+        mListener.register();
+    }
+
+    protected final void notifyUnregister() {
+        assert mListener != null;
+        mListener.unregister();
+    }
+
+    protected void init(Listener listener) {
+        mListener = listener;

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

move this line of code to constructor and make this function abstract

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

we should be able to pass the registration policy to the
NetworkChangeNotifierAutoDetect (NCNAD) (e.g. BackgroundSyncNetworkObserver
actually uses NCNAD on its own). so I introduced this method to solve the
chicken-egg problem regarding constructors.

+    }
+
+    protected abstract void destroy();
+}