ServiceWorker: Use TRACE_EVENT_WITH_FLOW for tracing fetch events

TRACE_EVENT is currently used but TRACE_EVENT_WITH_FLOW makes it easier to
track the flow of fetch events.

Bug: 860394
Change-Id: I7aa669ee3769763c31f6b8621bbb1bb466c17ae0
Reviewed-on: https://chromium-review.googlesource.com/1156334
Reviewed-by: Makoto Shimazu <shimazu@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Momoko Hattori <momohatt@google.com>
Cr-Commit-Position: refs/heads/master@{#579761}
1 file changed