[Fuchsia] Teardown WebComponents if their underlying Frame disconnects.

- Implement window.close() to teardown the Frame when the web content
  requests to.
- Fix WebComponent to trigger teardown of the Component when its
  underlying Frame disconnects.

The order of WebContentsDelegate API overrides are tweaked, to match
the order in WebContentsDelegate itself.

Bug: b/133176803
Change-Id: Iee49962b2b45dacb05b5ec8d329b5cd0805cba0b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1659597
Commit-Queue: Wez <wez@chromium.org>
Auto-Submit: Wez <wez@chromium.org>
Reviewed-by: Fabrice de Gans-Riberi <fdegans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#669419}
4 files changed