message: Added ability to handle client-side asserts in graphics tests
diff: import { PNG } from 'pngjs';
  import {
  Browser,
  + ConsoleMessage,
  launch as launchPuppeteer,
  LaunchOptions,
  Page,
  @@ -50,6 +51,13 @@ export class Screenshoter {
  errors.push(error.message);
  });
  + page.on('console', (message: ConsoleMessage) => {
  + const type = message.type();
  + if (type === 'error' || type === 'assert') {
  + errors.push(`Console ${type}: ${message.text()}`);
  + }
  + });
  +
  page.on('response', (response: Response) => {
  if (!response.ok()) {
  errors.push(`Network error: ${response.url()} status=${response.status()}`);
  