GN: Manually search path for Python

This manually searches the path for python rather than executing "cmd" to find it. This saves about 80ms in run time.

Review URL: https://codereview.chromium.org/1462393003

Cr-Original-Commit-Position: refs/heads/master@{#360981}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 30069efcdbf27248a74fcdcf59e4c08df1d75765
1 file changed
tree: 77855d1406f715f4bccb73c58f547dfde3832f26
  1. tools/