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..210f4d8a3c38d83d36aee7ad54d65635be94e558 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),
+      protocol_negotiation_(PN_UNKNOWN) {
 }
 
 // static
@@ -232,4 +234,22 @@ std::vector<uint8_t> SSLClientSocket::SerializeNextProtos(
   return wire_protos;
 }
 
+void SSLClientSocket::RecordProtocolNegotiation() {
+  if (protocol_negotiation_ == PN_UNKNOWN)
+    return;
+  std::string proto;
+  SSLClientSocket::NextProtoStatus status = GetNextProto(&proto);
+  if (status == kNextProtoUnsupported)
+    return;
+  if (status == kNextProtoNoOverlap) {
+    DCHECK(protocol_negotiation_ != PN_ALPN);
+    protocol_negotiation_ = PN_NPN_NO_OVERLAP;
+  }
+  NextProto protocol_negotiated = SSLClientSocket::NextProtoFromString(proto);
+  UMA_HISTOGRAM_SPARSE_SLOWLY(
+      "Net.SSLProtocolNegotiation",
+      static_cast<base::HistogramBase::Sample>(protocol_negotiation_) +
+          static_cast<base::HistogramBase::Sample>(protocol_negotiated));
+}
+
 }  // namespace net