relevant part of the video 5:23 - 6:25
https://youtu.be/E3gS9tjACwU?t=5m23s

Unable to reproduce the issue on chrome reported version# 69.0.3473.0 using Windows-10 with steps mentioned below:
1) Launched chrome reported version and clicked on '+' symbol at left top
2) Able to click the '+' button

@Reporter: Please find the attached screencast for your reference and provide your feedback on it.

Thanks!

Deleted: 857078.mp4 1.5 MB

	857078.mp4 1.5 MB View Download

Thank you for providing more feedback. Adding the requester to the cc list.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

you didn't understand what's the issue, the button works,
but it's not clickable from the top left pixel 0,0 in LTR or top right pixel 0,WIDTH_OF_SCREEN in RTL.
you can see in the video when you hover on it, it's a circular button, called floating action button "FAB" in material design, and it's far from the corner of the window, unlike the X button, FAB was designed for small touch screens with thumbs, I never saw a FAB in a top corner, but I don't know if it's allowed by the MD spec,
  - on Desktop, at least on Windows, the center of the circle should be on the pixels above and the icon offseted from the center. 
this new design, with this proposed change, is the most usable design from UX prespective on Desktop with mouses and no touch screen. watch that minute from the linked video in comment 1#, you'll understand. 

but why is it back to it's previous position on
Google Chrome	69.0.3479.0 (Official Build) canary (32-bit) (cohort: Clang-32)
Revision	4bd5a86d51d03f2c430547762c7a25a1a7946720-refs/branch-heads/3479@{#1}
OS	Windows
JavaScript	V8 6.9.256

a fixed position is better, an unfixed variable position is less usable.
it's the right design choice, aside from it being more usable and less cognitively demanding, it's future compatible, in the future you might add an option to have title/tab bar on the bottom, in ChromeOS at least, similar to Windows 10's new feature, tabs in all apps.  
and on Chrome mobile you might move the tree dots/burger menu to an expanding FAB button on the bottom L/R corner. then the + button becomes a standard familiar FAB, and familiar across all platforms.

I hope you adopt this better design. even though I will never use it, I use Chrome on desktop and only use shortcuts and vimium, no mouse.

wesam.wesam.co@ Thanks for the update.

As per comment #7, this looks to be a improvement request for new Material design. 
Hence marking this as Untriaged for further updates from dev.

Thanks..

Chrome already uses material design, it's Google's design specification (https://material.io/design) which is now popular and ubiquitous, this feature request is more compatible with the spec.