Revert "Disable fieldtrial config for FontSrcLocalMatching on Windows"

This reverts commit dcf25ed5.

Re-enable field trial config on Windows for FontSrcLocalMatching
after bot testing has stabilzied, see issue 996167.

Note to sheriffs: Should you see crashes or issues with
DWriteFontLookupTableBuilder or testing issues relating to matching
@font-face: { src: local() } fonts on Windows, in particular Windows 7,
please only revert this CL, preferably not the related one:
https://chromium-review.googlesource.com/c/chromium/src/+/1777862 -
if you can't reach drott@, try getting in touch with etienneb@ please
before reverting. Thanks.

Bug: 999787
Change-Id: I47a18fc1c31d0879700378a8924aff23de64997a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1787614
Commit-Queue: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Etienne Bergeron <etienneb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#694249}

testing/variations/fieldtrial_testing_config.json

@@ -2468,7 +2468,8 @@
                 "android_webview",
                 "chromeos",
                 "linux",
-                "mac"
+                "mac",
+                "windows"
             ],
             "experiments": [
                 {