chrome/test/media_router/resources/local_media_sink.json

{
  // Define the return value for getAvailableSinks API defined in
  // TestProvider.js.
  "getAvailableSinks": {
    // This is the URN used by LOCAL_FILE casting mode
    "urn:x-org.chromium.media:source:tab:0": [
      {"id": "id1", "friendlyName": "test-sink-1"},
      {"id": "id2", "friendlyName": "test-sink-2"}
    ]
  }
}