[bfcache] Add test filters to watchlist

R=ahemery@chromium.org

Change-Id: Ib82b3c0861673822f79445df58db9429b3d72ffd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1847333
Commit-Queue: Alexander Timin <altimin@chromium.org>
Commit-Queue: Arthur Hemery <ahemery@chromium.org>
Auto-Submit: Alexander Timin <altimin@chromium.org>
Reviewed-by: Arthur Hemery <ahemery@chromium.org>
Cr-Commit-Position: refs/heads/master@{#703671}

WATCHLISTS

@@ -245,7 +245,8 @@
       'filepath': 'content/browser/frame_host/back_forward_cache.*|'\
                   'content/browser/back_forward_cache_browsertest.cc|'\
                   'content/test/data/back_forward_cache/|'\
-                  'content/public/browser/back_forward_cache.*',
+                  'content/public/browser/back_forward_cache.*|'\
+                  'testing/buildbot/filters.bfcache.*.filter',
     },
     'binary_size': {
       'filepath': 'build/android/binary_size/|'\