Seen on: 59.0.3070.0 canary, but has likely been around for a while

Steps to reproduce:
1. Close all windows.
2. Align shelf to the bottom (though bug does repro for other alignments).
3. Position finger directly underneath the system tray, then swipe upwards to invoke the shelf 'stretch' animation.

What happens:
A highlight (ripple) appears within the system tray bounds and remains visible throughout the entire shelf-stretch animation.

What should happen instead:
The highlight should disappear as soon as the shelf begins to stretch.


Notes:

* Also reproduces for other buttons in the status tray area (status tray, notification center, VK button, opt-in IME button, etc), the overflow button in the shelf, and the launcher. (In the case of the launcher, the highlight actually persists after the stretching animation has ended.)

* If you follow the repro steps with at least one open window (i.e., omit step (1)), then the bug reproduces when swiping to reveal a hidden shelf, but does NOT repro when swiping to hide a visible shelf.

* It is expected that a highlight will begin to appear at the point where the finger comes in contact with the button but before the shelf-stretch animation begins. But once the animation begins the highlight should disappear; this expected behavior can be seen when swiping to hide a visible shelf with at least one window open.