Measure how often DNS hostnames aren't in preferred name form.

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index afbb320f6169c03e5ba62096ab69e9026ba728cb..f4d27bf51327165a1958f3b47323f3b6af89ae5e 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -38032,6 +38032,17 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>True if a URLRequest's referrer is empty or valid when set.</summary>
 </histogram>
 
+<histogram name="Net.ValidDNSName" enum="Boolean">
+  <owner>palmer@chromium.org</owner>
+  <summary>
+    True if a DNS name contains only characters for which
+    |net::IsValidLabelCharacter| returns true. Used to see if we can deprecate
+    and remove support for arbitrary bytes in DNS names. This histogram is
+    recorded when converting dotted DNS names into DNS query form, in
+    preparation for issuing a DNS request.
+  </summary>
+</histogram>
+
 <histogram name="Net.WebSocket.DeflateMode"
     enum="WebSocketNewPerMessageDeflateContextTakeoverMode">
   <owner>yhirano@chromium.org</owner>