This is also happening with the play/pause button.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/d8d4d846aa4cfc03352e374ea69e10a62c95a420

commit d8d4d846aa4cfc03352e374ea69e10a62c95a420
Author: Tommy Steimel <steimel@chromium.org>
Date: Wed Jan 17 03:32:37 2018

Prevent MediaControls from going into buffering state unnecessarily

This CL adds a check in the MediaControlsImpl::State method to only
return kBuffering when the video doesn't have enough data. This solves
an issue where the controls would flash into the buffering state
unnecessarily.

Bug:  794597 
Change-Id: If071bc35f199936f55168e07c11cb3fe5f139664
Reviewed-on: https://chromium-review.googlesource.com/865960
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#529576}
[modify] https://crrev.com/d8d4d846aa4cfc03352e374ea69e10a62c95a420/third_party/WebKit/Source/modules/media_controls/MediaControlsImpl.cpp