code: function createInjectionShim(scriptUrl, workerId) {
      // Hacky handling for blob URLs.
      // Unfortunately Chrome doesn't like importScript on blobs inside of the
      // workers, so we need to embed it.
      var resolvedScriptUrl = null;
      var scriptContents = null;
      if (goog.string.startsWith(scriptUrl, 'blob:')) {
        var xhr = new (goog.global['XMLHttpRequest']['raw'] || XMLHttpRequest)();
        xhr.open('GET', scriptUrl, false);
        xhr.send();
        scriptContents = xhr.response;
      } else {
        resolvedScriptUrl = goog.Uri.resolve(baseUri, scriptUrl).toString();
      }
  
      var shimScriptLines = [
        'this.WTF_WORKER_ID = ' + workerId + ';',
        'this.WTF_WORKER_BASE_URI = "' + goog.global.location.href + '";',
        'importScripts("' + wtfUrl + '");',
        'wtf.trace.prepare({',
        '});',
        'wtf.trace.start();'
      ];
  
      // Add the script import or directly embed the contents.
      if (resolvedScriptUrl) {
        shimScriptLines.push('importScripts("' + resolvedScriptUrl + '");');
      } else if (scriptContents) {
        shimScriptLines.push('// Embedded: ' + scriptUrl);
        shimScriptLines.push(scriptContents);
      }
  
      var shimBlob = new Blob([shimScriptLines.join('\n')], {
        'type': 'text/javascript'
      });
      var shimScriptUrl = goog.fs.createObjectUrl(shimBlob);
  
      return shimScriptUrl;
    }
docs: Creates a shim script that injects WTF.
  @param {string} scriptUrl Source script URL.
  @param {number} workerId Unique worker ID.
  @return {string} Shim script URL.