Using a ReportingObserver to watch for deprecation warnings on page.

reporting_observer.js

/**
 * @author ebidel@ (Eric Bidelman)
 * License Apache-2.0
 */

// Drop this in the DevTools console:
 
(new ReportingObserver((reports, observer) => {
  console.warn('This page is using deprecated APIs or features:');
  const deprecations = reports.map(report => {
    return {
      url: report.url,
      message: report.body.message,
      lineNumber: report.body.lineNumber || '-',
      colNumber: report.body.columnNumber || '-',
      anticipatedRemoval: report.body.anticipatedRemoval ? (new Date(report.body.anticipatedRemoval)).toLocaleDateString() : '-',
    };
  });
  console.table(deprecations);
}, {types: ['deprecation'], buffered: true})).observe();