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Add a test that exercises behavior for a webRequestBlocking listener
that never returns, and then the tab is closed. Do this with two
flavors:
- A listener in the extension's background page, where the
  RenderProcessHost is shutdown.
- A listener in an extension tab, which is then closed.

Verify that in both cases, navigation is unblocked when the extension
listener goes away.

Inspired by, but not in any way a fix for, https://crbug.com/877543.

Change-Id: Id918d6d5f7bf5d8235f1386ef48838bffaa1b50c
Reviewed-on: https://chromium-review.googlesource.com/1188942
Commit-Queue: Devlin <rdevlin.cronin@chromium.org>
Reviewed-by: Nasko Oskov <nasko@chromium.org>
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594509}