Fixed bubble bar options menu background.

Set the menu items background color in code.

Fixes: 353655843
Fixes: 356931191
Flag: com.android.wm.shell.enable_bubble_bar
Test: Manual. Open bubble bar menu. Switch theme. Open bubble bar menu
again. Repeat 5 times. Observe menu items background is correct.
Press lower or upper menu item and wait while ripple animation reaches
the end. Observe it does not spread beyond the corners. Screenshot:
https://screenshot.googleplex.com/jg5p9jedUbXdJCs

Change-Id: I92a7a1a6acf8350cb74bca2029f5e6392c42237c