emsdk

Include psutil module in the python build to enable emrun to track when browser process finishes. (#1464)

Without this, emrun web server will be left running after user code
quits the page abnormally without calling `exit()` (e.g. due to a page
awwsnap crash), and there are multiple processes in use by the browser.

emrun has a graceful fallback to weaker browser process detection when
psutil is not available, so this is easy to miss if not running emrun
with --verbose:
https://github.com/emscripten-core/emscripten/blob/814ec05f74eac9025c0442f51fa09bd8d02f8b43/emrun.py#L330-L339