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[ServiceWorker] Integrate trace events in embedded worker instance

Currently all the TRACE_EVENT* do not manage well in
embedded_worker_instance.cc, this CL integrates them to track
duration for every step throughout one complete starting worker process.

Also uses TRACE_EVENT_NESTABLE_ASYNC_* to replace deprecated
TRACE_EVENT_ASYNC*.

BUG=none

Review-Url: https://codereview.chromium.org/2821253002
Cr-Commit-Position: refs/heads/master@{#466888}