This adds a square next to the label in the status bar that serves
as a legend for the tick. The square background re-uses the colors
of the ticks, and those colors are overridden in High Contrast Mode,
using non-system but highly contrasted colors from a palette that
was created by the accessibility team.
In order for the ticks to be visible, we need to make sure that the
background canvas is displayed, and also the call to colorToRGBA needed
a document to properly handle system colors.
Differential Revision: https://phabricator.services.mozilla.com/D223473
f8685f56a2