message: Dispose document when tearing down JSDom environment
diff: @@ -97,6 +97,8 @@ class JSDOMEnvironment {
  if (this.errorEventListener) {
  this.global.removeEventListener('error', this.errorEventListener);
  }
  + // Dispose "document" to prevent "load" event from triggering.
  + Object.defineProperty(this.global, 'document', {value: null});
  this.global.close();
  }
  this.errorEventListener = null;
  