Keep workerStart timing info over request job restarts
In ServiceWorkerControlleeRequestHandler, job_ may be created multiple
times, or cleared (for example, when the request falls back to network).
In those cases, the workerStart timing info should hold the first time
SW started for the request.
This patch makes ServiceWorkerControlleeRequestHandler remember the
workerStart time from the first job.
BUG=465640
TEST=Will be added in https://codereview.chromium.org/1152673004/
Review URL: https://codereview.chromium.org/1160883004
Cr-Commit-Position: refs/heads/master@{#331766}
3 files changed
