src/vs/workbench/services/textMate/electron-sandbox/textMateWorker.ts/TextMateWorker/getOrCreateGrammar
class TextMateWorker:	public async getOrCreateGrammar(languageId: LanguageId): Promise<ICreateGrammarResult | null> {
		const grammarFactory = await this._grammarFactory;
		if (!grammarFactory) {
			return Promise.resolve(null);
		}
		if (!this._grammarCache[languageId]) {
			this._grammarCache[languageId] = grammarFactory.createGrammar(languageId);
		}
		return this._grammarCache[languageId];
	}