message: Always expect generationTimeMs
diff: @@ -148,6 +148,9 @@ class Analytics {
  }
  trackPageChange(generationTimeMs) {
  + if (typeof generationTimeMs !== 'number') {
  + throw new Error('Analytics.trackPageChange: expected generationTimeMs to be a number');
  + }
  if (this.disabled) return;
  if (this.firstPage) {
  // De-duplicate first page
  @@ -156,9 +159,7 @@ class Analytics {
  return;
  }
  this._paq.push(['setCustomUrl', getRedactedUrl()]);
  - if (typeof generationTimeMs === 'number') {
  this._paq.push(['setGenerationTimeMs', generationTimeMs]);
  - }
  this._paq.push(['trackPageView']);
  }
  