Just to clarify a bit, this isn't an issue with the Greenworks plugin (we're not using that) but it is a problem either with the later versions of NW.js or Chromium.
I've cut everything out of the loop (so no Greenworks, no Steam, no overlay or Construct 2), and tried using a simple set up including Christywl's basic example (which was confirmed to be working) in this bug report https://github.com/nwjs/nw.js/issues/5871 and just running nw from the command line. I just get a completely white screen when --in-process-gpu is added to the package.json chromium-args, if it is using nw.js 0.34 or above, and it works fine on 0.33.3 and below. So that isn't related to the Steam overlay, it just doesn't render anything at all.
We thought it probably best to give a heads up that some people might run into issues with that workaround and the current versions of nw.js for Construct 2. It may not be everybody that encounters this but it is certainly an issue on my system. I've not done any investigation into it at all, I'd guess probably a chromium issue, I'll try and spend some time on it when I get the chance and raise it as a bug report.