UserAgent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.82 Safari/537.36

Steps to reproduce the problem:
1. Checkout https://github.com/timroes/chrome-dev-tools-test
2. Run `gulp` in the project to startup a backend server (port 3000) and a reverse proxy (port 3001) that will just forward to the backend server (see also gulpfile)
3. Access localhost:3000 and look into DevTools Source tab. You will see that the sourcemap loaded fine (see attached via-backend.png screenshot). You can see the sources.
4. Access localhost:3001 and look into the DevTools.

What is the expected behavior?
You should also see on localhost:3001 the source files and the mapping should be loaded.

What went wrong?
As you can see in attached via-proxy.png, there are no sources shown even though it just forwarded to the backend.
Also the sample logs all requests at the proxy (and backend) you will see, that no request for the map file has been made, when accessing via localhost:3001. And you can see the request for the map file when you access via localhost:3000.

I also looked into the source-code of http-proxy-middleware if it filters out map files or something similar, but it doesn't seem to. Also I added log output to the very first line in the middleware where the request arrive, and also there no request for the map file arrives.

I also looked into gulp-connect, but it doesn't seem to filter out mappings at all - and when accessing gulp-connect via localhost:3000 it serves the map file just fine.

Did this work before? N/A 

Chrome version: 52.0.2743.82  Channel: stable
OS Version: Archlinux x64
Flash Version: -

Since there currently is no possibility anymore to debug the request for the mapping file from Chrome side, I don't know where to look into, to check if that is really a Chrome Dev Tool problem, but at least in Firefox the same sample scenario works just fine.
 

Deleted: via-proxy.png 43.2 KB

	via-proxy.png 43.2 KB View Download

Deleted: via-backend.png 39.9 KB

	via-backend.png 39.9 KB View Download