src/vs/workbench/contrib/welcome/walkThrough/common/walkThroughContentProvider.ts/WalkThroughSnippetContentProvider/textBufferFactoryFromResource
class WalkThroughSnippetContentProvider:	private async textBufferFactoryFromResource(resource: URI): Promise<ITextBufferFactory> {
		let ongoing = this.loads.get(resource.toString());
		if (!ongoing) {
			ongoing = new Promise(async c => {
				c(createTextBufferFactory(await requireToContent(resource)));
				this.loads.delete(resource.toString());
			});
			this.loads.set(resource.toString(), ongoing);
		}
		return ongoing;
	}