src/vs/editor/browser/widget/codeEditorWidget.ts/CodeEditorWidget/popUndoStop
class CodeEditorWidget:	public popUndoStop(): boolean {
		if (!this._modelData) {
			return false;
		}
		if (this._configuration.options.get(EditorOption.readOnly)) {
			// read only editor => sorry!
			return false;
		}
		this._modelData.model.popStackElement();
		return true;
	}