Add infrastructure for connected device group.

The core thing is to find out a way to update group when devices
(bt device and usb device)are updated.

The infrastructure contains three parts:
1. ConnectedDeviceController
Normal PreferenceController. Get info from sub controller and update
the preferenceGroup.

2. BluetoothDeviceUpdater
Listen to bluetooth callback, decide whether to add/remove devices

3. DevicePreferenceCallback
Interface to add/remove preference. This interface will be used in
ConntectedDeviceController and future SavedDeviceController

Bug: 69333961
Test: RunsettingsRoboTests
Change-Id: I85a9ef216a801d5f0dd1cf0130d53850a68be4bd

src/com/android/settings/connecteddevice/DevicePreferenceCallback.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settings.connecteddevice;
+
+import android.support.v7.preference.Preference;
+
+/**
+ * Callback to add or remove {@link Preference} in device group.
+ */
+public interface DevicePreferenceCallback {
+    /**
+     * Called when a device(i.e. bluetooth, usb) is added
+     * @param preference present the device
+     */
+    void onDeviceAdded(Preference preference);
+
+    /**
+     * Called when a device(i.e. bluetooth, usb) is removed
+     * @param preference present the device
+     */
+    void onDeviceRemoved(Preference preference);
+}