Remove status return from all uirenderer::Renderer functions

This moves the interface closer to android::Canvas. The only use of
return values was in the OpenGLRenderer subclass; that is replaced
with an internal dirty flag: returned from finish(), checked by
CanvasContext.

This is part of a series of CLs to refactor the Graphics JNI bindings.

BUG:15672762
R=djsollen@google.com,ccraik@google.com

Change-Id: Ifd533eb8839a254b0d3a5d04fc5a2905afdfc89e