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These should not start the reporter but are possible. Due to the
statefulness of WTR this means we need a new "has valid start time"
flag which controls when reporting is running.

BUG=965820,967103
TEST=new unittest
R=sandersd

Change-Id: Ieeb125472609f2a0c3b027c9c43ab4ded7cb669a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1632893
Auto-Submit: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Dan Sanders <sandersd@chromium.org>
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663930}