Using the per-revision bisect providing the bisect results,
Good build: 56.0.2913.0 (Revision: 430459).
Bad build: 56.0.2914.0 (Revision: 430837).

You are probably looking for a change made after 430806 (known good), but no later than 430807 (first known bad).
CHANGELOG URL:
  https://chromium.googlesource.com/chromium/src/+log/aeabb467b50c9de6fdf15fcd30d25ca83a3a6bee..4e7f02ab96450571468d5ab4730d396d63f192eb

@tyoshino -- Could you please look into the issue, pardon me if it has nothing to do with your changes and if possible please assign it to concern owner.

Thank You.

Adding RB Label as this is a recent Regression. Please remove if not required.
Thank You.

Still able to reproduce the issue on Ubuntu 14.04,Win 10.0 & Mac 10.11.6 using latest chrome version 57.0.2926.0.

tyoshino@ Could you please look into this issue.

Thanks!

tyoshino@, Can we get an update on this please

Sorry. I'll check.

Sorry that I didn't check this earlier. But 4e7f02ab96450571468d5ab4730d396d63f192eb must not be the cause. It's only removing unused "using" statements.

This doesn't reproduce here on
- Linux ToT local build (at r435209, debug build)
- Windows canary release 57.0.2936.0

I also downloaded r430806 (mentioned above as known good), r430826 (a bit newer than the one mentioned above as first known bad), r433062 (picked from recent builds) from continuous build and tried it, but the issue didn't reproduce on Linux.

Tested on Mac 10.11.6 and Windows 10 using latest chrome canary M57 #57.0.2943.0 &57.0.2942.0  and issue is still reproduced.

Note : Issue is not seen on Linux OS.

jshanbal@ is this still happening in latest M57 and M56?

jshanbal@ Could you please update on comment#10.

Thank you!

With response to comment #10, above issue is still reproducible on latest canary version 57.0.2956.0 

Issue is still seen on win latest canary 57.0.2969.0 

tyoshino@, Could you please take a look or route to appropriate dev if this is not due to your change.

Still able to reproduce the issue on Win 10.0 using latest chrome version 57.0.2984.0.

Could some one from dev team please look into this issue.

Thanks!

Just to update, still able to reproduce this issue on mac 10.12.2 using latest canary #58.0.2990.0.

Could anyone from dev team please have a look into this issue.

Thanks...!!

I'm able to reproduce on Linux 65.0.3292.0.  It seems that if you hover on the Waterfall header and there is a blue bar at the mouse position behind it, I can trigger the popup when it shouldn't trigger.

I will take a look.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/acd71e533085b2c17438ee75d70ec16dc5be489e

commit acd71e533085b2c17438ee75d70ec16dc5be489e
Author: Erik Luo <luoe@chromium.org>
Date: Thu Jan 11 20:37:34 2018

DevTools: fix hovered node when hovering over waterfall header

Popups and context menus depend on the currently hovered waterfall
row. The waterfall canvas rests behind the column header, so users do
not expect hovering on the header to trigger a popup for the row
behind.

Bug:  666206 
Change-Id: I14a8d9f4bc510ae20476ed91e9ffe003603edc74
Reviewed-on: https://chromium-review.googlesource.com/858477
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Erik Luo <luoe@chromium.org>
Cr-Commit-Position: refs/heads/master@{#528740}
[modify] https://crrev.com/acd71e533085b2c17438ee75d70ec16dc5be489e/third_party/WebKit/Source/devtools/front_end/network/NetworkWaterfallColumn.js

Update : 
Verified this issue on Windows (7,8,8.1,10),Linux (14.04 LTS),Mac OS X(10.12.6,10.13.1,10.13.3) OS with latest Canary build #65.0.3319.0 and the issue is fixed.
Kindly review an attached screen-cast.

Thank You!

Deleted: Actual_Devtools.mp4 660 KB

	Actual_Devtools.mp4 660 KB View Download