Is there a way to test this without the headset?

Worth noting is that a "fullscreen" feature was enabled recently that broke the screen dimensions. A revert landed here: https://chromium.googlesource.com/chromium/src.git/+/466d40a9545e8124e2ce2561146d46aceec23420

Yes, you need to add '--enable-vr-shell-dev' command line flag, and then the system menu should have a button for entering vr (at the very bottom after 'Help & Feedback').

That will default to using a cardboard configuration which means a gaze cursor and screen tap should work.

I usually use m.youtube.com to verify video in vr, but any video site should work.

And yes we were aware of the other fullscreen feature, that broke vr for a different reason, see  issue 729068 .

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a4ab2b3a0adc017cfe2d0ab19ad2092bf3beabb7

commit a4ab2b3a0adc017cfe2d0ab19ad2092bf3beabb7
Author: Matthew Jones <mdjones@chromium.org>
Date: Tue Jun 13 00:19:11 2017

[Home] Fix vr dimensions in Chrome Home

This change modifies the fullscreen manager's concept of whether or
not the browser controls should modify the viewport to depend on
the whether or not VR is active.

BUG= 722543 ,  730772 

Change-Id: I00770dffe6d278232d9e8a0d7ee5dd9be9c01a87
Reviewed-on: https://chromium-review.googlesource.com/528521
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#478837}
[modify] https://crrev.com/a4ab2b3a0adc017cfe2d0ab19ad2092bf3beabb7/chrome/android/java/src/org/chromium/chrome/browser/fullscreen/ChromeFullscreenManager.java

I tried this in canary 61.0.3129.0 and was not able to repro.  Fullscreen video in VR looks good even with Chrome Home enabled.  Thanks for the fix!

Verified in Chrome Canary 61.0.3138.0