Code review comment for lp:~vanvugt/mir/judder

This reintroduces eglSwapBuffers() blocking for buffers that are not rendered by the real compositors (i.e. for surfaces that are either occluded or off screen). That is, it only keeps eglSwapBuffers() running when all monitors are off. This can't be a long term solution if we want eglSwapBuffers() to be non-blocking in general, although perhaps it can serve as a workaround for our Qt 5.2 issues.

For a proper solution we need a more fine-grained approach, making decisions per renderable. Chris' approach https://code.launchpad.net/~raof/mir/1hz-rendering-always/+merge/216246 does this an the SwitchingBundle level, but we can achieve the same results at the MultiThreadedCompositor level. I will work on a proposal for that and we can decided on the best approach.