The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7ed5e122b1f7cf16fc0ddec769d493c76db1e679

commit 7ed5e122b1f7cf16fc0ddec769d493c76db1e679
Author: Liquan(Max) Gu <maxlg@chromium.org>
Date: Tue May 15 02:55:36 2018

[UserTimingL3] performance.mark API returns mark entry

For ergonomic purpose, UserTimingL3 supports returning the measure/mark
entry they created. It's also useful for feature detection of L3 API
as well.

Bug:  842770 
Change-Id: I4dfa1abb87d6f5750be7f9a23123530a1bf45e74
Reviewed-on: https://chromium-review.googlesource.com/1057995
Reviewed-by: Ojan Vafai <ojan@chromium.org>
Reviewed-by: Timothy Dresser <tdresser@chromium.org>
Commit-Queue: Liquan (Max) Gǔ <maxlg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#558594}
[modify] https://crrev.com/7ed5e122b1f7cf16fc0ddec769d493c76db1e679/third_party/WebKit/LayoutTests/http/tests/performance-timing/custom-user-timing/po-customusertiming-featuredetection.html
[modify] https://crrev.com/7ed5e122b1f7cf16fc0ddec769d493c76db1e679/third_party/blink/renderer/core/timing/performance.cc
[modify] https://crrev.com/7ed5e122b1f7cf16fc0ddec769d493c76db1e679/third_party/blink/renderer/core/timing/performance.h
[modify] https://crrev.com/7ed5e122b1f7cf16fc0ddec769d493c76db1e679/third_party/blink/renderer/core/timing/performance.idl
[modify] https://crrev.com/7ed5e122b1f7cf16fc0ddec769d493c76db1e679/third_party/blink/renderer/core/timing/performance_user_timing.cc
[modify] https://crrev.com/7ed5e122b1f7cf16fc0ddec769d493c76db1e679/third_party/blink/renderer/core/timing/performance_user_timing.h