Note, does not repro with sites that use custom media controls. E.g. http://video.disney.com/watch/coco-official-final-trailer-55d1da01a6e16bed0b47e5a6

Aldo, likely related to your input changes?

If this was related to input, I don't see why it would happen in some sites but not others. From my observations trying to reproduce the issue, it actually seems that youtube is particularly slow in VR, so that feedback for the click takes some time to show up. dbbrooks, do you agree on this?

I just checked to see if they were just delayed, but that's not the case for what I'm seeing here. Even if I wait a while (5 - 10 seconds), some clicks just don't register at all. And it's a frequent occurrence. And confirmed that on the same phone, with a different Chrome version (M68), there's no repro. 

Turns out that this is not specific to a video player. 

Just go to a page with some links. I find that going to the webvr samples page https://webvr.info/samples/, selecting the 360 presentation, entering then exiting WebVR is a good way to clearly notice it. Since the Enter VR button is so large, when you click on it and nothing happens, it's very clear.

And as Aldo has pointed out, it does depend on "how" your thumb is using the trackpad. Mine seems to trigger it very easily.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5aa63e066731a6df12bf27d727fd912cdfd083cf

commit 5aa63e066731a6df12bf27d727fd912cdfd083cf
Author: Aldo Culquicondor <acondor@chromium.org>
Date: Fri Jul 13 17:19:33 2018

Increase touch slop when entering/leaving VR

VR input devices behave like laser pointers, leading to movements with
lower precision as opposed to a mouse or a touchpad, due to natural
shakiness of users. This change increases the slop when on VR browsing,
as a factor of the platform's slop.

Bug:  860321 
Change-Id: I47906921ab41e69b7bc4e427ebbd327ae8f7d9bf
Reviewed-on: https://chromium-review.googlesource.com/1134088
Commit-Queue: Aldo Culquicondor <acondor@chromium.org>
Reviewed-by: Timothy Dresser <tdresser@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574957}
[modify] https://crrev.com/5aa63e066731a6df12bf27d727fd912cdfd083cf/content/browser/renderer_host/render_widget_host_view_android.cc
[modify] https://crrev.com/5aa63e066731a6df12bf27d727fd912cdfd083cf/ui/events/gesture_detection/filtered_gesture_provider.cc
[modify] https://crrev.com/5aa63e066731a6df12bf27d727fd912cdfd083cf/ui/events/gesture_detection/filtered_gesture_provider.h
[modify] https://crrev.com/5aa63e066731a6df12bf27d727fd912cdfd083cf/ui/events/gesture_detection/gesture_provider_config_helper.cc
[modify] https://crrev.com/5aa63e066731a6df12bf27d727fd912cdfd083cf/ui/events/gesture_detection/gesture_provider_config_helper.h