SF: Add support for screen captures

Add Layer::drawNow to support capturing portions
of the screen in the FE, as this is not tied
to vsync

Test: Compile/Run manually
Merged-Id: I0781d44240ae127a6e70b35282a02cbedfe36fe4
Change-Id: I0781d44240ae127a6e70b35282a02cbedfe36fe4