Use time tolerance in run_code_generation check. The mtime values I was seeing on my file system were sometimes floating point numbers that were very very close but not exactly the same. This might be due to numerical errors. Increasing the tolerance to something still very small, precision is less than a second. It will lead to fewer rebuilds of non-dirty files. Bug: angleproject:2455 Change-Id: I95dc3214ee91af7a70a20cc625405e0e2bc18698 Reviewed-on: https://chromium-review.googlesource.com/1032855 Reviewed-by: Luc Ferron <lucferron@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>