build/lib/optimize.ts/loader
function loader(src: string, bundledFileHeader: string, bundleLoader: boolean): NodeJS.ReadWriteStream {
	let sources = [
		`${src}/vs/loader.js`
	];
	if (bundleLoader) {
		sources = sources.concat([
			`${src}/vs/css.js`,
			`${src}/vs/nls.js`
		]);
	}

	let isFirst = true;
	return (
		gulp
			.src(sources, { base: `${src}` })
			.pipe(es.through(function (data) {
				if (isFirst) {
					isFirst = false;
					this.emit('data', new VinylFile({
						path: 'fake',
						base: '.',
						contents: Buffer.from(bundledFileHeader)
					}));
					this.emit('data', data);
				} else {
					this.emit('data', data);
				}
			}))
			.pipe(concat('vs/loader.js'))
	);
}