message: Make the Resize Canary stop observing the element on disconnect.
diff: /*
  - * Copyright 2019 Simon Edwards <simon@simonzone.com>
  + * Copyright 2020 Simon Edwards <simon@simonzone.com>
  *
  * This source code is licensed under the MIT license which is detailed in the LICENSE.txt file.
  */
  @@ -48,6 +48,11 @@ export class ResizeCanary extends HTMLElement {
  });
  }
  + disconnectedCallback(): void {
  + const container = <HTMLDivElement> getShadowId(this, ID_SIZER);
  + ResizeCanary._resizeNotifier.unobserve(container);
  + }
  +
  private _createNodes(): Node {
  return htmlToFragment(trimBetweenTags(`<style>
  #${ID_CONTAINER} {
  