Add remote volume slider to sound settings

1. Add RemoteVolumePreferenceController to control volume through
MediaSessions.
2. Add related preference to skip calling AudioManager.

Bug: 126199571
Test: RunSettingsRoboTests
Change-Id: I9cb85ccf5f49be6d127cb61caf445b2ee7dfb579

src/com/android/settings/notification/RemoteVolumeSeekBarPreference.java

@@ -0,0 +1,56 @@
+/*
+ * 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.notification;
+
+import android.content.Context;
+import android.util.AttributeSet;
+
+/**
+ * A slider preference that controls remote volume, which doesn't go through
+ * {@link android.media.AudioManager}
+ **/
+public class RemoteVolumeSeekBarPreference extends VolumeSeekBarPreference {
+
+    public RemoteVolumeSeekBarPreference(Context context, AttributeSet attrs, int defStyleAttr,
+            int defStyleRes) {
+        super(context, attrs, defStyleAttr, defStyleRes);
+    }
+
+    public RemoteVolumeSeekBarPreference(Context context, AttributeSet attrs, int defStyleAttr) {
+        super(context, attrs, defStyleAttr);
+    }
+
+    public RemoteVolumeSeekBarPreference(Context context, AttributeSet attrs) {
+        super(context, attrs);
+    }
+
+    public RemoteVolumeSeekBarPreference(Context context) {
+        super(context);
+    }
+
+    @Override
+    public void setStream(int stream) {
+        // Do nothing here, volume is not controlled by AudioManager
+    }
+
+    @Override
+    protected void init() {
+        if (mSeekBar == null) return;
+        updateIconView();
+        updateSuppressionText();
+    }
+}