constructor( json, dracoLoader ) {

		if ( ! dracoLoader ) {

			throw new Error( 'THREE.GLTFLoader: No DRACOLoader instance provided.' );

		}

		this.name = EXTENSIONS.KHR_DRACO_MESH_COMPRESSION;
		this.json = json;
		this.dracoLoader = dracoLoader;
		this.dracoLoader.preload();

	}
DRACO Mesh Compression Extension

Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_draco_mesh_compression

@private