[Telemetry] Restart browser in the case it hangs during unittests.
[Telemetry] Restart browser in the case it hangs during unittests.

This should unstick us if a unittest times out in a weird way.

BUG=418577

Review URL: https://codereview.chromium.org/645233002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#299216}

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