Auto merge of #472 - vvuk:master, r=glennw
Auto merge of #472 - vvuk:master, r=glennw

Add runtime profiler toggle and expose DebugRenderer

This is a bit of a hack, so let me know if you'd prefer me to not do this, or do this a different way.  I'm using this in https://github.com/vvuk/wrench/commit/0747956617902b0ea5c1cb14463c07cd5004bb7c to provide on-screen help and toggle the profiler at runtime.    Toggling the profiler seems to work well.

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