Using the per-revision bisect providing the bisect results,
Good build: 56.0.2899.0 (Revision: 426989)
Bad build: 56.0.2900.0 (Revision: 427219)

You are probably looking for a change made after 427136 (known good), but no later than 427137 (first known bad).

CHANGE-LOG URL:
---------------------------------------
https://chromium.googlesource.com/chromium/src/+log/10336a25975c113e068268d848b01f0c3563f215..aac459cb9f155cfe4f330d31616b5d6081042de7

From the CL above, assigning the issue to the concern owner

@spqchan: 
------------------
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.

Review-Url: https://codereview.chromium.org/2430403003

Note : Mac Specific issue.

as this is recent regression adding RBS, please change if required.

This is too close to stable and the severity isn't high enough for M56, punting to M57

Unable to replicate the issue on Mobile device (Tablet and Handset) as the steps provided cannot be followed on it.

Devices Used:
=============
Device name: Samsung Galaxy S7 (Handset)
Chrome version Used: Beta - 56.0.2924.68
Android Version: 6.0.1 / MMB29K

Device name : Samsung Galaxy Tab 3 Lite (Tablet)
Chrome version Used: Beta - 56.0.2924.68
Android Version: 4.4.4 / KTU84P 

Reasons: 
========
1) The appearance of permission bubble is different on Android device than that displayed on a desktop. 
2) The full screen functionality is different comparing an Android and a Desktop(On Android - Scrolling down the page automatically hides the tab strip, On Desktop - We have specific full screen option or shortcut). 
3) No escape button is available on an android device.

P.S: Also tried by checking the option "Request desktop site", Cannot replicate the issue.

@sdy, since you said you're taking some UI bugs, can you work on this? Feel free to reassign to me if you don't want to. Thanks!

sdy@ : Issue still seen on 58.0.3000.0, could you please take a look into this and update further.As its marked as Stable blocker.

A friendly reminder that M57 Stable is launch is coming soon! Your bug is labelled as Stable ReleaseBlock, pls make sure to land the fix and get it merged into the release branch ASAP so it gets enough baking time in Beta (before Stable promotion). Thank you!

This should not block stable.

Friendly ping!!
Sdy@,
Still we are able to reproduce the issue on mac 10.12.2 using latest Canary-58.0.3018.0.
Could you please look into this issue & update the thread.
Thanks!!

Ping received. This is in my queue, but I have higher priority bugs ahead of it.

Update:

***Mass UI Triage***

We were unable to reproduce this bug on latest Canary version #72.0.3611.0 as 'Cmd+Alt+F' shortcut key doesn't respond on browser fullscreen from the page. If this bug still reproduces for you, please reopen or file a new issue.

Thanks!