Sort events for average lag using timestamp

AverageLagTracker expects information about events are fed into it in
order, so events in a frame should be sorted before being passed to it.
Currently, this sorting is based on event's trace id. Instead we can use
timestamp of event to sort them. This way, we don't need to keep track
of trace ids for events which is one step towards moving average lag
metrics tracking off of ui::LatencyInfo.

Bug: 1101000
Change-Id: I77acae9d254280c3d97ca404f94832f811d99ede
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3138363
Commit-Queue: Mohsen Izadi <mohsen@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#919498}

• cc/metrics/average_lag_tracker.h[diff]
• cc/metrics/average_lag_tracker_unittest.cc[diff]
• cc/metrics/average_lag_tracking_manager.cc[diff]