Add histogram to track NPN/ALPN.

net/socket/ssl_client_socket.cc

Index: net/socket/ssl_client_socket.cc
diff --git a/net/socket/ssl_client_socket.cc b/net/socket/ssl_client_socket.cc
index 4aacbc8d42db5faa1f4eb25cad3588efb37b752f..1235ed800f05ab3210991e4e42b074a5015257df 100644
--- a/net/socket/ssl_client_socket.cc
+++ b/net/socket/ssl_client_socket.cc
@@ -5,6 +5,7 @@
 #include "net/socket/ssl_client_socket.h"
 
 #include "base/metrics/histogram.h"
+#include "base/metrics/sparse_histogram.h"
 #include "base/strings/string_util.h"
 #include "crypto/ec_private_key.h"
 #include "net/base/host_port_pair.h"
@@ -19,7 +20,8 @@ SSLClientSocket::SSLClientSocket()
       protocol_negotiated_(kProtoUnknown),
       channel_id_sent_(false),
       signed_cert_timestamps_received_(false),
-      stapled_ocsp_response_received_(false) {
+      stapled_ocsp_response_received_(false),
+      negotiation_extension_(kExtensionUnknown) {
 }
 
 // static
@@ -124,6 +126,11 @@ void SSLClientSocket::set_protocol_negotiated(NextProto protocol_negotiated) {
   protocol_negotiated_ = protocol_negotiated;
 }
 
+void SSLClientSocket::set_negotiation_extension(
+    SSLNegotiationExtension negotiation_extension) {
+  negotiation_extension_ = negotiation_extension;
+}
+
 bool SSLClientSocket::WasChannelIDSent() const {
   return channel_id_sent_;
 }
@@ -232,4 +239,28 @@ std::vector<uint8_t> SSLClientSocket::SerializeNextProtos(
   return wire_protos;
 }
 
+void SSLClientSocket::RecordNegotiationExtension() {
+  if (negotiation_extension_ == kExtensionUnknown)
+    return;
+  std::string proto;
+  SSLClientSocket::NextProtoStatus status = GetNextProto(&proto);
+  if (status == kNextProtoUnsupported)
+    return;
+  // Convert protocol into numerical value for histogram.
+  NextProto protocol_negotiated = SSLClientSocket::NextProtoFromString(proto);
+  base::HistogramBase::Sample sample =
+      static_cast<base::HistogramBase::Sample>(protocol_negotiated);
+  // In addition to the protocol negotiated, we want to record which TLS
+  // extension was used, and in case of NPN, whether there was overlap between
+  // server and client list of supported protocols.
+  if (negotiation_extension_ == kExtensionNPN) {
+    if (status == kNextProtoNoOverlap) {
+      sample += 1000;
+    } else {
+      sample += 500;

[davidben, 2014/10/03 17:55:07]

This is probably worth a comment in net/socket/next_proto.h that the values must
be below 500 now.

[Bence, 2014/10/10 15:26:10]

Done.

+    }
+  }

[davidben, 2014/10/03 17:55:07]

Nit: I'd put in an
  } else {
    DCHECK_EQ(kExtensionALPN, negotiation_extension_);
  }
just so you document that the other case is ALPN.

[Bence, 2014/10/10 15:26:10]

Done.

+  UMA_HISTOGRAM_SPARSE_SLOWLY("Net.SSLProtocolNegotiation", sample);
+}
+
 }  // namespace net