Fix loading ring overlapping problem

By design, the loading ring is in the middle of the recycler view.
In the Android S, recyclerview isn't matched the screen's height.
So, if the recyclerview doesn't contains any item, the height could be
very low and then it causes to overlaps with drop down view.

The simple solution is to fix height of view of progress
bar, so it won't rely on the height of recycler view anymore.

Fix: 184643347
Test: Go to app notification page, and no overlapping problem.
Change-Id: I9f4fddba0254ac0cb0ba0b128a7dcc2de05d1fce