Add metrics detecting anomalously high ZIP compression ratios

It's possible for a single ZIP entry to be very large, even if we only
scan small ZIP archives. These metrics will measure how often that occurs.

Bug: 980940
Change-Id: I481952db86ca96e96d372a0f0eb6115ce2fcffbf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1688017
Commit-Queue: Daniel Rubery <drubery@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Varun Khaneja <vakh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#677877}
2 files changed