Supportleanbackshowcase: Polishing 2 and transition performance fix

Move background of browse/details/music from layout to windowBackground.
Setting background on view will cause the whole RelativeLayout being
faded in while transition move content inside the RelativeLayout.
The RelativeLayout does not have a hardwarelayer, nor does it specify
hasOverlappingRendering=false.  This falls to the slowest rendering
path.

Change-Id: I78bacc965e641d7f960aae5cf212c29f6b1f0f11
5 files changed