core: add support for translucent volume panel

Add support for display the volume panel in translucent mode

Patchset 4: Make it depends to high-end graphics flag

Change-Id: I4f21a6cc88282789072a0e71ae696b754a5e083e
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>

Conflicts:
	core/java/android/view/VolumePanel.java