Enable stencil clipping within clearLayerRegions

bug:18538502

Cherry-pick of adc0d9da from AOSP

Previously stencil clipping within clearLayerRegions is disabled by commit
62d307c2. However, clearing whole layer
regions causes black-colored triangle regions when a TextView has
RotateAnimation because the draw within clearLayerRegions does not
affected by the current stencil clip.

Change-Id: Id32a0b16754b109905f833e063ebfa156bd953f2
Signed-off-by: Dohyun Lee <dohyun.lee@lge.com>