The post_build_ninja_summary.py script, which autoninja automatically
runs if NINJA_SUMMARIZE_BUILD=1 is set, summarizes build time by file
extension. This is a good default summary but it can be handy to create
additional output categories. This change allows using fn_match style
wildcards to create additional categories which will then be summarized.
For instance:

  python post_build_ninja_summary.py -C out/Def -s prec*.obj;blink*.obj

In addition the chromium_step_types environment variable can be set so
that when autoninja runs this script there will be additional summary
categories.

This has been used most recently when measuring the cost of creating and
using blink precompiled header files.

Bug: 1061326
Change-Id: I080b4ddd06d045a2351220e202cd9eec111bf00e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2093145
Auto-Submit: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>