Contains some internal refactoring, no externally observable
changes.

TBR=tandrii@chromium.org, iannucci@chromium.org
BUG=1051724

Change-Id: I921c1a4adaa877dda07357463b4bb3f7dfc66676
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2288657Reviewed-by: Vadim Shtayura <vadimsh@chromium.org>
Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Vadim Shtayura <vadimsh@chromium.org>