loadTexture( textureIndex ) {

		const json = this.json;
		const options = this.options;
		const textureDef = json.textures[ textureIndex ];
		const sourceIndex = textureDef.source;
		const sourceDef = json.images[ sourceIndex ];

		let loader = this.textureLoader;

		if ( sourceDef.uri ) {

			const handler = options.manager.getHandler( sourceDef.uri );
			if ( handler !== null ) loader = handler;

		}

		return this.loadTextureImage( textureIndex, sourceIndex, loader );

	}
Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#textures

@private
@param {number} textureIndex
@return {Promise<THREE.Texture|null>}