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