src/vs/workbench/api/browser/mainThreadDocuments.ts/MainThreadDocuments/_doCreateUntitled
class MainThreadDocuments:	private async _doCreateUntitled(associatedResource?: URI, languageId?: string, initialValue?: string): Promise<URI> {
		const model = await this._textFileService.untitled.resolve({
			associatedResource,
			languageId,
			initialValue
		});
		const resource = model.resource;
		if (!this._modelTrackers.has(resource)) {
			throw new Error(`expected URI ${resource.toString()} to have come to LIFE`);
		}
		this._proxy.$acceptDirtyStateChanged(resource, true); // mark as dirty
		return resource;
	}