st chromeHelper = model.getOrCreateHelper(
        tr.model.helpers.ChromeModelHelper);
    if (chromeHelper === undefined) return chromeBounds;
    for (const helper of chromeHelper.browserHelpers) {
      if (helper.mainThread) {
        chromeBounds.addRange(helper.mainThread.bounds);
      }
    }
    for (const pid in chromeHelper.rendererHelpers) {
      if (chromeHelper.rendererHelpers[pid].mainThread) {
        chromeBounds.addRange(
            chromeHelper.rendererHelpers[pid].mainThread.bounds);
