function GLTFTextureDDSExtension() {

  if (!THREE.DDSLoader) {

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

  }

  this.name = EXTENSIONS.MSFT_TEXTURE_DDS;
  this.ddsLoader = new THREE.DDSLoader();

}
DDS Texture Extension

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