Support BetterTogether feature flags in services code.

Bug: b/255495104
Test: N/A
Change-Id: I042c21730e4821e64d17b12e9cdaaaaf7b4c310c

services/core/java/com/android/server/media/MediaFeatureFlagManager.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright (C) 2023 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.server.media;
+
+import android.annotation.StringDef;
+import android.provider.DeviceConfig;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+/* package */ class MediaFeatureFlagManager {
+
+    /**
+     * Namespace for media better together features.
+     */
+    private static final String NAMESPACE_MEDIA_BETTER_TOGETHER = "media_better_together";
+
+    @StringDef(prefix = "FEATURE_", value = {
+        FEATURE_IS_USING_LEGACY_BLUETOOTH_CONTROLLER
+    })
+    @Target({ ElementType.TYPE_USE, ElementType.TYPE_PARAMETER })
+    @Retention(RetentionPolicy.SOURCE)
+    /* package */ @interface MediaFeatureFlag {}
+
+    /**
+     * Whether to use old legacy implementation of BluetoothRouteController or new
+     * 'Audio Strategies'-aware controller.
+     */
+    /* package */ static final @MediaFeatureFlag String
+            FEATURE_IS_USING_LEGACY_BLUETOOTH_CONTROLLER =
+            "BluetoothRouteController__enable_legacy_bluetooth_routes_controller";
+
+    private static final MediaFeatureFlagManager sInstance = new MediaFeatureFlagManager();
+
+    private MediaFeatureFlagManager() {
+        // Empty to prevent instantiation.
+    }
+
+    /* package */ MediaFeatureFlagManager getInstance() {
+        return sInstance;
+    }
+
+    /**
+     * Returns a boolean value from {@link DeviceConfig} from the system_time namespace, or
+     * {@code defaultValue} if there is no explicit value set.
+     */
+    public boolean getBoolean(@MediaFeatureFlag String key, boolean defaultValue) {
+        return DeviceConfig.getBoolean(NAMESPACE_MEDIA_BETTER_TOGETHER, key, defaultValue);
+    }
+}