Replace Debug.WriteLine

`Debug.WriteLine` is only there in debug session, but the information it prints could be useful in other scenarios, such as production debugging. Some alternatives, in increasing order of preference:
1. [Trace.TraceInformation](https://msdn.microsoft.com/en-us/library/system.diagnostics.trace.traceinformation(v=vs.110).aspx) / [Trace.TraceWarning](https://msdn.microsoft.com/en-us/library/system.diagnostics.trace.tracewarning(v=vs.110).aspx) / [Trace.TraceError](https://msdn.microsoft.com/en-us/library/system.diagnostics.trace.traceerror(v=vs.110).aspx).
2. Same as above but using your own [TraceSource](https://msdn.microsoft.com/en-us/library/system.diagnostics.tracesource(v=vs.110).aspx)
3. [EventSource](https://msdn.microsoft.com/en-us/library/system.diagnostics.tracing.eventsource(v=vs.110).aspx) (ETW).

Start with a repository-wide search for `Debug.WriteLine` and review each usage in context. Compare the listed `Trace` and `EventSource` alternatives, choose an approach that supports production diagnostics, and verify that the relevant debug output has been replaced without losing useful information.

Written by the indexing model from the issue text.