Updates npm_test to work on Windows
Updates npm_test to work on Windows

process.env.PWD does not exist on Windows, so we default to asking for
the current working directory there instead.

TBR=tvanderlippe@chromium.org

Change-Id: I35ba848aee686ed066bf095afa3d05b45f527139
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2102715
Reviewed-by: Paul Lewis <8915f5d5c39a08c5a3e8a8d7314756e4580816f9@chromium.org>
Commit-Queue: Paul Lewis <8915f5d5c39a08c5a3e8a8d7314756e4580816f9@chromium.org>

ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend,ChromeDevTools/devtools-frontend