When UiHelper is set to translucent with setOpaque(false), the
target SurfaceView's surface is set to be composited on top of
the activity's window. There are situations however where one
may want to render regular Views on top of the SurfaceView.
The new setMediaOverlay() API allows exactly that: when this
property is enabled, rendering to a translucent target will
cause the SurfaceView's surface to be composited above other
surfaces, but below the activity's surface.
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