[cc/metrics] Move ThreadType into FrameSequenceMetrics.

This change relocates the ThreadType enum into FrameSequenceMetrics,
and uses that when it reports a metric, to make it easier to handle
(in follow-up CLs) rather than strings.

BUG=none

Change-Id: I86795334a4d43aaf516361d1fb7b7474ef150d56
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1965999
Auto-Submit: Sadrul Chowdhury <[email protected]>
Reviewed-by: Xida Chen <[email protected]>
Commit-Queue: Sadrul Chowdhury <[email protected]>
Cr-Commit-Position: refs/heads/master@{#724633}
5 files changed