Coverage updates are sent as deltas, and this means that it
is very important that the consumer gets /all/ updates;
otherwise, the coverage information will be wrong.

Previously, we introduces the ability into the back-end to
send triggered updates, i.e. updates that are triggered by
the back-end at interesting points in time. These updates
are delivered via an event, and any consumer must process
these events.

This CL introduces a flag to startPreciseCoverage that
controls whether the back-end is allowed to send such
triggered updates on its own initiative. The default is
`false` to maintain backwards compatibility with consumers
that don't yet handle the events.

Bug: chromium:1022031
Change-Id: Ie36a92a3b627b19ea4041f1b8da1ec66c6b9b771
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2043798Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66232}