add wrapper to make GYP_PARALLEL=1 work

add wrapper to make GYP_PARALLEL=1 work for build\gyp_chromium

This is a workaround for multiprocessing on Windows. Importing in Python on
Windows doesn't search for imports that don't end in .py (and aren't
directories with an __init__.py). So, add this wrapper to avoid having
people change their command line to add a .py when running gyp_chromium.

R=dmazzoni@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=160151

[dmazzoni, 2012-10-04 17:16:53]

lgtm

Nice! Mike Wittman had just identified the same root cause, but I was figuring I
might have to do the opposite (rename gyp_chromium -> gyp_chromium.py, update a
lot of stuff...) - this is much simpler!