Needed to find *.winmd files for UWP build.

This CL and crrev.com/c/2007881 were used to generate the recent
toolchains with UWP support:
b92fff97f2e0323e99803f37f4b77b843bdbf69d in crrev.com/c/2015984 and
9ff60e43ba91947baca460d0ca3b1b980c3a2c23 in crrev.com/c/2025528.

Bug: chromium:1032635
Change-Id: I1ab0b6e11a30600deb377078815c268d8f9027e4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2013579
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>