The NINJA_SUMMARIZE_BUILD already triggers two types of build
performance data - setting NINJA_STATUS to give more details during the
build and running post_build_ninja_summary.py after the build.

One of the most common causes of slow builds is when CreateProcess
becomes slow, usually due to anti-virus overhead. Neither of these
reports make this problem easily visible, but ninja -d stats does. In
particular the StartEdge data is an excellent summary of CreateProcess
timing. If the StartEdge average (avg) is more than about 6,000 us
(6.0 ms) it might be worth investigating why.

Therefore this change makes it so that autoninja.py adds -d stats to the
command line when NINJA_SUMMARIZE_BUILD is set to 1.

Change-Id: I1b6b990708c784a2cd71d153713b422f090775e6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1788399Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Bruce Dawson <brucedawson@chromium.org>