Make Net.DNS.SecureDnsMode.*.TotalTime histograms visible in metrics.

There was a spurious base="true" tag on these histograms. Landing this
change on ToT is sufficient.

Bug: 1004409, 985589
Change-Id: I9790c88eecca045d7faf2e5bcf19e1389eb5a8d5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1807579Reviewed-by: Eric Orth <ericorth@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Commit-Queue: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#696937}

tools/metrics/histograms/histograms.xml

@@ -75000,8 +75000,8 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram base="true" name="Net.DNS.SecureDnsMode.Automatic.TotalTime"
-    units="ms" expires_after="M81">
+<histogram name="Net.DNS.SecureDnsMode.Automatic.TotalTime" units="ms"
+    expires_after="M81">
   <owner>dalyk@google.com</owner>
   <owner>doh-core@google.com</owner>
   <summary>
@@ -75012,7 +75012,7 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram base="true" name="Net.DNS.SecureDnsMode.Off.TotalTime" units="ms"
+<histogram name="Net.DNS.SecureDnsMode.Off.TotalTime" units="ms"
     expires_after="M81">
   <owner>dalyk@google.com</owner>
   <owner>doh-core@google.com</owner>
@@ -75024,7 +75024,7 @@ uploading your change for review.
   </summary>
 </histogram>
 
-<histogram base="true" name="Net.DNS.SecureDnsMode.Secure.TotalTime" units="ms"
+<histogram name="Net.DNS.SecureDnsMode.Secure.TotalTime" units="ms"
     expires_after="M81">
   <owner>dalyk@google.com</owner>
   <owner>doh-core@google.com</owner>