Add missing annotation to annotations.xml

TBR=rhalavati@chromium.org

Bug: 954181
Change-Id: I7ff96420ad497cf4e3afc740a352b544dbccd386
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1572560
Commit-Queue: Nicolas Ouellet-Payeur <nicolaso@chromium.org>
Reviewed-by: Nicolas Ouellet-Payeur <nicolaso@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652177}

tools/traffic_annotation/summary/annotations.xml

@@ -244,6 +244,7 @@ Refer to README.md for content description and update process.
  <item id="service_worker_update_checker" hash_code="130931413" type="0" content_hash_code="46608086" os_list="linux,windows" file_path="content/browser/service_worker/service_worker_single_script_update_checker.cc"/>
  <item id="services_http_server_error_response" hash_code="59302801" type="0" content_hash_code="127774041" os_list="linux,windows" file_path="services/network/public/cpp/server/http_server.cc"/>
  <item id="sigined_exchange_cert_fetcher" hash_code="79442849" type="0" content_hash_code="8138156" os_list="linux,windows" file_path="content/browser/web_package/signed_exchange_cert_fetcher.cc"/>
+<item id="sigined_exchange_validity_pinger" hash_code="57114284" type="0" content_hash_code="119482488" os_list="linux,windows" file_path="content/browser/web_package/signed_exchange_validity_pinger.cc"/>
  <item id="signed_in_profile_avatar" hash_code="108903331" type="0" content_hash_code="72850619" os_list="linux,windows" file_path="chrome/browser/profiles/profile_downloader.cc"/>
  <item id="socket_bio_adapter" hash_code="516551" type="0" content_hash_code="21643352" os_list="linux,windows" file_path="net/socket/socket_bio_adapter.cc"/>
  <item id="spdy_push_stream" hash_code="36915753" type="0" content_hash_code="69224629" os_list="linux,windows" file_path="net/spdy/spdy_session.cc"/>