Use real screen size to scale duration

Duration scale based on screen size was using the area of the screen
excluding system bars to compare with our reference device's screen
size. This caused the following issues:
1) On baseline device (i.e N5) a scaling factor that is not 1 will be
   applied to the duration.
2) Scaling on the same device will be different in landscape vs.
   portrait, as the system bars take different amounts of space in
   different orienations.

This CL fixes both of the above issues.

Bug: 20309042

Change-Id: I9d1d0a471d968bee1330b80f0f69a0066d6a1860