Add another DoH service to hardcoded upgrade mapping.

Bug: 1018373
Change-Id: I9261f794749e250bd08265cf32596d6a2a766e36
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1879204
Commit-Queue: Katharine Daly <dalyk@google.com>
Reviewed-by: Eric Orth <ericorth@chromium.org>
Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709641}

net/dns/dns_util.cc

@@ -174,6 +174,12 @@ const std::vector<DohUpgradeEntry>& GetDohUpgradeList() {
                "1dot1dot1dot1.cloudflare-dns.com"} /* DoT hostname */,
               {"https://chrome.cloudflare-dns.com/dns-query",
                true /* use-post */}),
+          DohUpgradeEntry("Comcast",
+                          {"75.75.75.75", "75.75.76.76", "2001:558:feed::1",
+                           "2001:558:feed::2"},
+                          {""} /* DoT hostname */,
+                          {"https://doh.xfinity.com/dns-query{?dns}",
+                           false /* use_post */}),
           DohUpgradeEntry(
               "Dnssb",
               {"185.222.222.222", "185.184.222.222", "2a09::", "2a09::1"},

tools/metrics/histograms/histograms.xml

@@ -169746,6 +169746,7 @@ regressions. -->
   <suffix name="CleanBrowsingFamily" label="CleanBrowsing family filter."/>
   <suffix name="CleanBrowsingSecure" label="CleanBrowsing secure filter."/>
   <suffix name="Cloudflare" label="Cloudflare."/>
+  <suffix name="Comcast" label="Comcast."/>
   <suffix name="Dnssb" label="Dns.sb."/>
   <suffix name="Google" label="Google."/>
   <suffix name="OpenDNS" label="OpenDNS standard service."/>