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..da2d6ba0c8d8a88fabe6ba53519e0b69f07e5926 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 +239,30 @@ 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;
+    }
+  } else {
+    DCHECK_EQ(kExtensionALPN, negotiation_extension_);
+  }
+  UMA_HISTOGRAM_SPARSE_SLOWLY("Net.SSLProtocolNegotiation", sample);

[jar (doing other things), 2014/10/11 01:13:59]

This is indeed the "right way" to get something akin to a 2D histogram.

+}
+
 }  // namespace net