message center: Make BoundedLabel override OnPaint instead of Paint.

This makes the BoundedLabel override View::OnPaint, allowing us to make
View::Paint non-virtual.

The functional difference is that Paint() calls PaintCommon() which:
 - Early outs if not visible
 - Paints any children

The BoundedLabel is used by NotificationView, but no children are ever
added to it and it's not exposed outside the class. So it's safe to
convert it to use OnPaint() and remove the visible early out.

R=dewittj@chromium.org, mukai@chromium.org, stevenjb@chromium.org
BUG=466426

Review URL: https://codereview.chromium.org/1035553002

Cr-Commit-Position: refs/heads/master@{#322082}
2 files changed