GitLab

When the download shelf appears the Show All button at the far right is
very dark, almost as if its been drawn several times on top of itself
(see the original bug report for a screenshot of the problem).

The problem is that the Show All button is layer backed (because the
shelf is), so it caches its contents. The Show All button also declares
itself to be opaque but wants the shelf background texture to show
through. It accomplishes this by simulating a lock focus onto the shelf
from within its drawRect:, and calling the shelf's drawRect:.

Unfortunately, when the button first draws (into its layer) the shelf
is hidden and so the shelf's height is 0.0. The shelf's drawing routines
restrict themselves to the shelf's bounds rect - that works most of the
time because if the shelf has 0 height there should be no drawing to be
done. This optimization doesn't work for the Show All button when it
uses the zero-height shelf to draw its background.

The proposed fix is to detect the zero-height shelf from within
drawRect:, and to use a frame-changed notification from the shelf as
the signal to request a redraw.

BUG=485782

Review URL: https://codereview.chromium.org/1125363005

Cr-Commit-Position: refs/heads/master@{#330120}