Rework receiver/dispatcher design slightly, and replace Layer usage.

Switched from 'renderer/info' to 'dispatcher/renderer' to make their
interaction more natural. The new BakedOpRenderer is more similar in
responsibilities to the OpenGLRenderer, as it manages layer and frame
lifecycles, and performs the actual rendering.

However, it's still simpler because the BakedOpDispatcher handles
mapping Canvas drawing ops to Glops, and the OpReorderer handles almost
all canvas state operations.

Also switch BakedOpRenderer to use the new OffscreenBuffer, which
serves as a lightweight Layer replacement, with a much simpler
lifecycle.

Change-Id: Ie0e2e248503400041d49729d813d485d28c76eb3