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When an error message has recurred several times, show a message on the
interstitial. Note: the message isn't styled yet; the feature is off by default
so I'll do the styling (and translation screenshot) in a follow-up CL.

Bug: 839969
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I94a31ff16eaf9e8ef82134f372852f03b19e28df
Reviewed-on: https://chromium-review.googlesource.com/1049119
Commit-Queue: Emily Stark <estark@chromium.org>
Reviewed-by: Christopher Thompson <cthomp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#557190}