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This is needed to show the events Waterfall.
I will implement the front end side later on.

Devtools for WebTransport design doc:https://bit.ly/3ig8BLi

Bug: 1152290
Change-Id: I7913c46961f911b0a3f9e8bab44c7e023b4abbd8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2576862Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Commit-Queue: Yoichi Osato <yoichio@chromium.org>
Cr-Commit-Position: refs/heads/master@{#834464}