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