Python3 upgrades Required to run run_code_generation.py on gLinux. Bug: angleproject:5707 Change-Id: Ifb416be6f89eb67faf43e7de66c6f9a92a5eb5e1 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3465514 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Cody Northrop <cnorthrop@google.com>