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Stores the profiler in TLS and registers trace log observer for the
thread. If tracing is enabled then IO thread will be profiled.
We observe a lot of janks on IO thread and stack traces will be useful
to debug these traces.

Change-Id: I84f5c5f9c15d957ac2ee807289ddfab24731ef6d
Reviewed-on: https://chromium-review.googlesource.com/c/1330748
Commit-Queue: ssid <ssid@chromium.org>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Reviewed-by: Mike Wittman <wittman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#608549}