Measure how often the users are encountering MD5...

net/base/connection_type_histograms.h

+// Copyright (c) 2008 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef NET_BASE_CONNECTION_TYPE_HISTOGRAMS_H_
+#define NET_BASE_CONNECTION_TYPE_HISTOGRAMS_H_
+
+// The UpdateConnectionTypeHistograms function collects statistics related
+// to the number of MD5 certificates that our users are encountering.  The
+// information will help us decide when it is fine for browsers to stop
+// supporting MD5 certificates, in light of the recent MD5 certificate
+// collision attack (see "MD5 considered harmful today: Creating a rogue CA
+// certificate" at http://www.win.tue.nl/hashclash/rogue-ca/).
+
+namespace net {
+
+enum ConnectionType {
+  CONNECTION_ANY = 0,      // Any connection, SSL or not
+  CONNECTION_SSL = 1,      // An SSL connection
+  CONNECTION_SSL_MD5 = 2,  // An SSL connection with an MD5 certificate in
+                           // the certificate chain (excluding root)
+  CONNECTION_SSL_MD2 = 3,  // An SSL connection with an MD2 certificate in
+                           // the certificate chain (excluding root)
+  CONNECTION_SSL_MD4 = 4,  // An SSL connection with an MD4 certificate in
+                           // the certificate chain (excluding root)
+  NUM_OF_CONNECTION_TYPES
+};
+
+void UpdateConnectionTypeHistograms(ConnectionType type);
+
+}  // namespace net
+
+#endif  // NET_BASE_CONNECTION_TYPE_HISTOGRAMS_H_