Reached out to ellyjones and tapted since some mouseevents (i.e. ET_MOUSE_RELEASED)  are not bubbling through cocoa to the views window.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/ebd76a8ccc62496cb23bd31ffe81514d88280fac

commit ebd76a8ccc62496cb23bd31ffe81514d88280fac
Author: Jennifer Apacible <apacible@chromium.org>
Date: Tue May 08 03:16:51 2018

[Picture in Picture] Update hit test point value for OverlayWindowFrame.

This change allows the user to interact with the window contents, most
notably the media controls. This also disables dragging on the window,
which is a lower priority to have compared to working media controls.

Previously, we were unable to interact with Mac controls. Other
platforms, such as Linux, required a double click to interact with them.

Manually tested on Mac OSX and Linux. Enabling dragging will be done in
a future patch.

BUG:  839721   836389 
Change-Id: Iddaa83d244c0b76760688d12e469afc9265d93a8
Reviewed-on: https://chromium-review.googlesource.com/1048394
Reviewed-by: Becca Hughes <beccahughes@chromium.org>
Commit-Queue: apacible <apacible@chromium.org>
Cr-Commit-Position: refs/heads/master@{#556669}
[modify] https://crrev.com/ebd76a8ccc62496cb23bd31ffe81514d88280fac/chrome/browser/ui/views/overlay/overlay_window_views.cc