Code review comment for lp://qastaging/~afrantzis/mir/buffer-bind-to-render-image

In summary, I think we need:

Platform code:
  GLBuffer allocate_gl_buffer();
  ShmBuffer allocate_shm_buffer(); // Should work on all platforms

Rendering code:
  Switch behaviour based on the type of buffer. e.g. a ShmBuffer can be released immediately after glTexImage2D. However a GLBuffer must be held till after swapbuffers as the driver is likely sharing memory.

Generic buffer queuing code:
  Can refer to them all as "Buffer" which is the base class of the things being queued.