Incrementally disentangles DisplayListRenderer and OpenGLRenderer. Introduces abstract CanvasStateClient class to share three functions between the two. Design doc at https://docs.google.com/a/google.com/document/d/1PY1JF7AfPEF2UOUAnETS5j_4_tnJShTAMExvpCJfP8o/edit?usp=sharing. BUG:15672762 R=djsollen@google.com,ccraik@google.com,jreck@google.com Change-Id: Ic9fdffe18808e7d921ad06d01ea1ca25b2ad6f23