See  bug 792527 .

Question about vpython: If a.py calls b.py via subprocess and a.py is invoked via vpython, does b.py inherit a.py's environment. I wonder if I can fix this bug by simply using vpython in ninja_wrapper.py:
https://codesearch.chromium.org/chromium/build/scripts/slave/recipe_modules/chromium/api.py?rcl=f51a223063a7c3f72dfbf19604babbec2876e392&l=252

Though, given how many steps in a compile, that may be non-trivial.