message: More minor cleanup.
diff: @@ -171,7 +171,7 @@ const registry: {[url: string]: Module} = Object.create(null);
  let pendingDefine: (() => [Array<string>, OnExecutedCallback | undefined])|
  undefined = undefined;
  let topLevelScriptIdx = 0;
  -let previousTopLevelUrl: string|undefined = undefined;
  +let previousTopLevelUrl: NormalizedUrl|undefined = undefined;
  let baseUrl = getBaseUrl();
  /** Begin loading a module from the network. */
  @@ -433,21 +433,20 @@ window.define = function(deps: string[], moduleBody?: OnExecutedCallback) {
  // state, because this is a top level document and it's already loaded.
  const mod = getModule(url) as ModuleG<StateEnum.Loading>;
  mod.isTopLevel = true;
  - const predecessor = previousTopLevelUrl;
  - previousTopLevelUrl = url;
  const waitingModule = beginWaitingForTurn(mod, deps, moduleBody);
  - if (predecessor !== undefined) {
  + if (previousTopLevelUrl !== undefined) {
  // type=module scripts execute in order (with the same timing as defer
  // scripts). Because this is a top-level script, and we are trying to
  // mirror type=module behavior as much as possible, wait for the
  // previous module script to finish (successfully or otherwise)
  // before executing further.
  - whenModuleTerminated(getModule(predecessor as NormalizedUrl), () => {
  + whenModuleTerminated(getModule(previousTopLevelUrl), () => {
  beginWaitingOnDeps(waitingModule);
  });
  } else {
  beginWaitingOnDeps(waitingModule);
  }
  + previousTopLevelUrl = url;
  }
  }, 0);
  };
  