Fix bug 5623642 - Status bar background incompatible with some legacy apps

Give some background protection to custom layouts in legacy notifications.

Pre-HC it was extremely common for apps to hardcode text colors in
layouts. Since this can lead to black text on a dark background in
HC/ICS, give these older apps that target SDK < 11 a light gray
background.

Change-Id: Iab3dea4beb9172b2f9a5cae53991cf952d0c8cde