function GLTFTextureDDSExtension( ddsLoader ) {

		if ( ! ddsLoader ) {

			throw new Error( 'THREE.GLTFLoader: Attempting to load .dds texture without importing THREE.DDSLoader' );

		}

		this.name = EXTENSIONS.MSFT_TEXTURE_DDS;
		this.ddsLoader = ddsLoader;

	}
DDS Texture Extension

Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Vendor/MSFT_texture_dds