Below is manual regression range and bisect info.

Good build: 64.0.3248.0
Bad build:  64.0.3249.0

You are probably looking for a change made after 511171 (known good), but no later than 511172 (first known bad).
CHANGELOG URL:
The script might not always return single CL as suspect as some perf builds might get missing due to failure.
  https://chromium.googlesource.com/chromium/src/+log/3e8787f26ce93e2ca110da7e511353e390010d08..ab702021c631e9d4a3b1858a86ee2a70c73ae04a

Suspect: https://chromium.googlesource.com/chromium/src/+/ab702021c631e9d4a3b1858a86ee2a70c73ae04a

@benjhayden: Kindly help to reassign, if your changes are not related to this isusue.

Kindly review the attached screen-cast for reference.

Deleted: Actual behavior.mp4 629 KB

	Actual behavior.mp4 629 KB View Download

Deleted: Expected behavior.mp4 233 KB

	Expected behavior.mp4 233 KB View Download

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

Still we are able to reproduce the issue on Windows 7, mac 10.12.6 & ubuntu 14.04 using chrome latest Canary-64.0.3273.3 as per C#0.

benjhayden@, Could you please check and update the bug accordingly as it is marked as stable blocker.
Thank you.

Culprit is:

https://chromium.googlesource.com/catapult.git/+/7d0ab7044d5ea2c71ba38e04a3161833ff93acd8

It still reverts cleanly.
People who need to look at flow events in a ToT developer build can just do this under the third_party/catapult directory:
git revert 7d0ab7044d5ea2c71ba38e04a3161833ff93acd8

benjhayden@,

Friendly ping to get an update on this issue as it is marked as stable blocker.

Thanks..!

M-64 branch point is only one day away.
I created a revert: https://chromium-review.googlesource.com/c/catapult/+/797390
Can't land it because I do not have review privileges in the catapult repository.

Could someone on the team just hit the button?

Really sorry about that, slipped off my radar. Just lgtm'd it.

Fix on CQ: https://chromium-review.googlesource.com/c/catapult/+/795110

Cool. Not clear whether DEPS will be rolled prior to branch. To be safe, let's keep this issue open until we've confirmed the revert was picked up in the M-64 DEPS.

Ah. Revert stopped just in time!

The following revision refers to this bug:
  https://chromium.googlesource.com/catapult/+/81d3bd9213f44aa05c1323e5b1cf648cea0d1950

commit 81d3bd9213f44aa05c1323e5b1cf648cea0d1950
Author: Ben Hayden <benjhayden@chromium.org>
Date: Wed Nov 29 18:15:56 2017

Fix "View Options" dropdown in trace viewer.

The tr-ui-b-dropdown dom-module encapsulates a modal dialog that drops down from
a button. When the user clicks outside of the modal dialog, it closes. When the
user clicks inside of the modal dialog, it should not close. Due to the way that
modal dialogs are implemented, clicking inside of the dialog produces the same
type of event as clicking outside of it, so it is common for modules such as
tr-ui-b-dropdown to compare the coordinates of the click event to the bounding
rect of the dialog in order to determine whether the click was inside or outside
of the dialog.

Polymer defines 'tap' events as a generalization of click events that support
touch screens as well as mouse pointers.  However, there is a crucial difference
between click events and polymer tap events: click event coordinates are given
by event.clientX and event.clientY, whereas tap event coordinates are given by
event.detail.x and event.detail.y.

When a recent change upgraded the click event handler to a tap event handler, it
failed to update the clientX/clientY references to point to the Polymer tap
event's detail.x/y.

This CL fixes the click-event-style clientX/clientY references to correctly
reference the tap-event-style detail.x/y. The new test fails without the fix.

Bug:  chromium:785138 
Change-Id: I006652066a2d56a6219757f1815bfe9bad7bb54e
Reviewed-on: https://chromium-review.googlesource.com/795110
Reviewed-by: Ethan Kuefner <eakuefner@chromium.org>
Commit-Queue: Ben Hayden <benjhayden@chromium.org>

[modify] https://crrev.com/81d3bd9213f44aa05c1323e5b1cf648cea0d1950/tracing/tracing/ui/base/dropdown_test.html
[modify] https://crrev.com/81d3bd9213f44aa05c1323e5b1cf648cea0d1950/tracing/tracing/ui/base/dropdown.html

This should be fixed. Do I need to request merge?