You are probably looking for a change made after 513360 (known good), but no later than 513361 (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/a28eb737c4c9424d7656ada19b688af854777968..1eca7aba022c190ea02e34dbd4ae52a8f5f88bbc

Suspecting: https://chromium.googlesource.com/chromium/src/+/1eca7aba022c190ea02e34dbd4ae52a8f5f88bbc
Could you please check whether this is caused with respect to your change, if not please help us in assigning it to the right owner.

Note: This is windows 10 touch device specific issue and not seen on other os.

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

Wow - nice find! This is indeed a problem. The TouchSelectionMenu is a `TouchSelectionMenuRunnerViews::Menu` which inherits from BubbleDialogDelegateView. - https://cs.chromium.org/chromium/src/ui/views/touchui/touch_selection_menu_runner_views.cc?q=TouchSelectionMenuRunnerViews::Menu&l=40

I suspect we want this particular bubble to be `immune` to the MD-anchoring logic and arrow-removal in bubble_border.cc. Maybe we can just set an appropriate existing, or new, arrow enum value.

That flag isn't rolling out in m64 (see  Issue 789770 ), so bumping the milestone. (and assigning to bsep to triage while I'm still buried in Mac stuff :/)

Load balancing

pkasting@ Gentle Ping! This issue is marked as RB-Stable for M65, could you please take a look in to this issue.

Thanks!

Load balancing

Allen: I don't have a touch device to verify, but if this doesn't reproduce pre-Harmony it can be untagged as RBS

kylixrd@,
Friendly ping to get an update as it is marked as M65-stable blocker.
Thanks..!

 Issue 804218  has been merged into this issue.

Only reproduces with Harmony flag on, so not RBS (we'll address it before launching).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d9affa23867a2b2d7c2dd5c984e27c52956dc563

commit d9affa23867a2b2d7c2dd5c984e27c52956dc563
Author: Allen Bauer <kylixrd@chromium.org>
Date: Tue Jan 30 15:20:01 2018

Chopped off touch selection menu in RTL after Harmony changes.

Fixed Widget::SetBoundsConstrained & ensured TouchSelectionMenuRunnerViews is clamped to the desktop bounds.

Bug:  791507 
Change-Id: I3386fc2a93bee2c10ce98ffa3b2974ab40b9606a
Reviewed-on: https://chromium-review.googlesource.com/888259
Commit-Queue: Allen Bauer <kylixrd@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#532880}
[modify] https://crrev.com/d9affa23867a2b2d7c2dd5c984e27c52956dc563/ui/views/touchui/touch_selection_menu_runner_views.cc
[modify] https://crrev.com/d9affa23867a2b2d7c2dd5c984e27c52956dc563/ui/views/widget/widget.cc

Update : 
Retested above issue on Windows(10 Touch)OS using latest Canary #66.0.3335.0 and issue is fixed. Now, touch selection menu appears properly and is not chopped. Kindly review the attached screen-cast.

Thank You!

Deleted: Current_Result.mp4 532 KB

	Current_Result.mp4 532 KB View Download