FB: Heads Up background color && transparency [2/2]

PS: manual rebase

PS: fix my retardedness

PS: fix heads up TRDS background resources

PS: clear content holder background prior to setting TRDS
        drawable so that correct drawable for TRDS state
        is set

PS: revert non-TRDS background to AOSP gray (default
        system notification background color)

PS: clean up some unused code
Change-Id: I3942c0ce178491e3429e5ae7eb24b43ba07a1f40