src/vs/platform/contextkey/browser/contextKeyService.ts/AbstractContextKeyService/createKey
class AbstractContextKeyService:	public createKey<T>(key: string, defaultValue: T | undefined): IContextKey<T> {
		if (this._isDisposed) {
			throw new Error(`AbstractContextKeyService has been disposed`);
		}
		return new ContextKey(this, key, defaultValue);
	}