Add mms preference and controller

Only visible when it is metered and mobile data off.
Also refactor one mobile data observer so we can reuse it.

Bug: 130222866
Test: RunSettingsRoboTests
Change-Id: Id218f51da3c373fad98c1a39cfadd6b0e8c46a88

src/com/android/settings/network/MobileDataContentObserver.java

@@ -0,0 +1,72 @@
+/*
+ * Copyright (C) 2019 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.network;
+
+import android.content.Context;
+import android.database.ContentObserver;
+import android.net.Uri;
+import android.os.Handler;
+import android.provider.Settings;
+import android.telephony.TelephonyManager;
+
+/**
+ * {@link ContentObserver} to listen to update of mobile data change
+ */
+public class MobileDataContentObserver extends ContentObserver {
+    private OnMobileDataChangedListener mListener;
+
+    public MobileDataContentObserver(Handler handler) {
+        super(handler);
+    }
+
+    public static Uri getObservableUri(int subId) {
+        Uri uri = Settings.Global.getUriFor(Settings.Global.MOBILE_DATA);
+        if (TelephonyManager.getDefault().getSimCount() != 1) {
+            uri = Settings.Global.getUriFor(Settings.Global.MOBILE_DATA + subId);
+        }
+        return uri;
+    }
+
+    public void setOnMobileDataChangedListener(OnMobileDataChangedListener lsn) {
+        mListener = lsn;
+    }
+
+    @Override
+    public void onChange(boolean selfChange) {
+        super.onChange(selfChange);
+        if (mListener != null) {
+            mListener.onMobileDataChanged();
+        }
+    }
+
+    public void register(Context context, int subId) {
+        final Uri uri = getObservableUri(subId);
+        context.getContentResolver().registerContentObserver(uri, false, this);
+
+    }
+
+    public void unRegister(Context context) {
+        context.getContentResolver().unregisterContentObserver(this);
+    }
+
+    /**
+     * Listener for update of mobile data(ON vs OFF)
+     */
+    public interface OnMobileDataChangedListener {
+        void onMobileDataChanged();
+    }
+}