I've uploaded a CL to fix this and added tests. Though, it's unclear how old this issue is :(

Issue 770898 has been merged into this issue.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/000d61dbcbee70739fee835b071707285b296cc1

commit 000d61dbcbee70739fee835b071707285b296cc1
Author: Mounir Lamouri <mlamouri@chromium.org>
Date: Mon Nov 20 16:11:33 2017

Cast Overlay: show the overlay if the video element is interacted with.

The overlay should show when the video is tapped or interacted with.

Bug:  785322 
Change-Id: I9ac249005cf08723c35fc6885070c7ec90234aae
Reviewed-on: https://chromium-review.googlesource.com/774459
Reviewed-by: Becca Hughes <beccahughes@chromium.org>
Commit-Queue: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517836}
[modify] https://crrev.com/000d61dbcbee70739fee835b071707285b296cc1/third_party/WebKit/Source/modules/media_controls/MediaControlsImpl.cpp
[modify] https://crrev.com/000d61dbcbee70739fee835b071707285b296cc1/third_party/WebKit/Source/modules/media_controls/MediaControlsImplTest.cpp
[modify] https://crrev.com/000d61dbcbee70739fee835b071707285b296cc1/third_party/WebKit/Source/modules/media_controls/elements/MediaControlOverlayEnclosureElement.cpp
[modify] https://crrev.com/000d61dbcbee70739fee835b071707285b296cc1/third_party/WebKit/Source/modules/media_controls/elements/MediaControlOverlayEnclosureElement.h