Record OSThread::trace_id() instead of OSThread::id() in profile samples.
Record OSThread::trace_id() instead of OSThread::id() in profile samples.

The profiler only uses the thread id to check if two samples with the
same timestamp belong to the same thread. Using trace_id() allows
profile samples to be correctly grouped with timeline events.

R=iposva@google.com

Review URL: https://codereview.chromium.org/1508233003 .

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