Makes sense.

What category should this be under? Possibly just "blink"?
Should these be async events? I think probably.

https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/frame/PerformanceMonitor.cpp?rcl=91d2e90881fc404976e1aa462d1d6a1681c0d687&l=262

thresholds_ are not set which make it impossible to report any long task, and there is no To-do to set these thresholds. Is it a bug?

Also curious why ReportLongTask is conditional upon two thresholds?

Oh sorry, there are some places to set these values, but haven't been indexed in code search.

I found that if not subscribed, the thresholds are all 0 to make it disabled, which means that reportLongTask is just for performance API's use.

questions:
Do we want to log the long tasks as trace event only when subscribing them or regardless of subscription?

Regardless of performance observer subscription, as this is for Devtools & traceviewer usage.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/26a60c2908155fcba28a21b1065d21adbc39a1c6

commit 26a60c2908155fcba28a21b1065d21adbc39a1c6
Author: maxlg <maxlg@chromium.org>
Date: Fri Jul 14 21:04:42 2017

Long tasks: add a trace event for long tasks

Add a trace event for long task entries, so this can be better surfaced in
devtools, traceviewer etc.

BUG= 738752 

Review-Url: https://codereview.chromium.org/2966073003
Cr-Commit-Position: refs/heads/master@{#486885}

[modify] https://crrev.com/26a60c2908155fcba28a21b1065d21adbc39a1c6/third_party/WebKit/Source/core/timing/Performance.cpp
[modify] https://crrev.com/26a60c2908155fcba28a21b1065d21adbc39a1c6/third_party/WebKit/Source/platform/scheduler/base/task_queue_manager.cc