function zoomChangeListener(zoomChangeInfo) {
  var settings_str = "mode:" + zoomChangeInfo.zoomSettings.mode +
      ", scope:" + zoomChangeInfo.zoomSettings.scope;

  console.log('[ZoomDemoExtension] zoomChangeListener(tab=' +
              zoomChangeInfo.tabId + ', new=' +
              zoomChangeInfo.newZoomFactor + ', old=' +
              zoomChangeInfo.oldZoomFactor + ', ' +
              settings_str + ')');
}
@fileoverview In this extension, the background page demonstrates how to
              listen for zoom change events.