src/vs/editor/common/services/languageService.ts/LanguageService/createByFilepathOrFirstLine
class LanguageService:	public createByFilepathOrFirstLine(resource: URI | null, firstLine?: string): ILanguageSelection {
		return new LanguageSelection(this.onDidChange, () => {
			const languageId = this.guessLanguageIdByFilepathOrFirstLine(resource, firstLine);
			return this._createAndGetLanguageIdentifier(languageId);
		});
	}