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This patch implements crash reporting, as detailed in the
reporting spec: https://w3c.github.io/reporting/#crash-report

Change-Id: I209880150193910a0947608e6b08a6eeea29206c
Reviewed-on: https://chromium-review.googlesource.com/1174965
Commit-Queue: Paul Meyer <paulmeyer@chromium.org>
Reviewed-by: Nick Carter <nick@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589941}