Record UMA metrics for Must-Staple certificates on private roots

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 bd68078331b8a6a56f6ce665f1da3772eb4126ce..a7b3c247d2b8ac13f0f8f5f3af259e740f97d922 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -28683,6 +28683,28 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Net.Certificate.TLSFeatureExtensionWithPrivateRoot"
+    enum="Boolean">
+  <owner>estark@chromium.org</owner>
+  <summary>
+    This histogram is recorded every time Chrome successfully verifies a
+    certificate that chains to a private root. A value of true indicates that
+    the certificate contains the TLS Feature Extension, and false indicates that
+    it doesn't.
+  </summary>
+</histogram>
+
+<histogram name="Net.Certificate.TLSFeatureExtensionWithPrivateRootHasOCSP"
+    enum="Boolean">
+  <owner>estark@chromium.org</owner>
+  <summary>
+    This histogram is recorded every time Chrome successfully verifies a
+    certificate that chains to a private root and the certificate contains the
+    TLS Feature Extension. A value of true indicates that the connection had an
+    OCSP response stapled, and a value of false indicates that it did not.
+  </summary>
+</histogram>
+
 <histogram name="Net.CertificatePinSuccess" enum="BooleanSuccess">
   <obsolete>
     Renamed to Net.PublicKeyPinSuccess 28 Oct 2011.