[Autofill Assistant] Shutdown when interstitial page shown or render process gone

For example,
Interstitial page is shown if it is blocked by safe browsing, like bad ssl.

Bug: 806868
Change-Id: I2f5f0ddfcc0b4efae6174772108b98697a383121
Reviewed-on: https://chromium-review.googlesource.com/c/1315707
Reviewed-by: Stephane Zermatten <szermatt@chromium.org>
Reviewed-by: Mathias Carlen <mcarlen@chromium.org>
Commit-Queue: Ganggui Tang <gogerald@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605687}