Highlight all BubbleIconView instances.

Highlights the BubbleIconView whenever the corresponding widget is
visible. This was previously a one-off done for the bookmark star view.

This addresses highlighting the translate icon, bookmark icon, zoom icon
and others in a single place. This makes it less error prone and more
future proof.

BubbleIconView still has to be added as an observer of the bubble widget
(but this is already required to remove button-press highlights when the
widget closes).

Bug: chromium:808273
Change-Id: Ibd4e14b4876be3e79ef8a85a0a9feade65aa5628
Reviewed-on: https://chromium-review.googlesource.com/905408


Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Bret Sepulveda <bsep@chromium.org>
Commit-Queue: Peter Boström <pbos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537928}