base

Move Snapshot management to intermediate StatefulBaseRenderer class

The eventual goal is for the StatefulBaseRenderer to serve as the
common base class between the DisplayListRenderer and OpenGLRenderer.

This will separate DisplayList recording, Snapshot stack management,
and the GL in OpenGLRenderer.

Additionally, avoid sp<> parameters, and use const parameters in
several places, with the intent of greatly reducing the surface area
where renderer subclasses can modify snapshot stack.

Next steps:
-move bulk of clipping logic into StatefulBaseRenderer
-disable direct snapshot access

Change-Id: Ibc3c6747134ec7daf8ea535866239fa73b874390