Introduce new SPDY Version UMA histogram.

net/socket/next_proto.cc

Index: net/socket/next_proto.cc
diff --git a/net/socket/next_proto.cc b/net/socket/next_proto.cc
index c9172365c383fec7e0a1089b3284fb1c0d7aa7cd..d7f8abb3c88ec86eee7f7f1bee0e0de6b3d94fef 100644
--- a/net/socket/next_proto.cc
+++ b/net/socket/next_proto.cc
@@ -2,10 +2,32 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "next_proto.h"
+#include "net/socket/next_proto.h"
+
+#include "base/logging.h"
 
 namespace net {
 
+unsigned int SpdyProtoPermanentValue(NextProto protocol) {
+  // These values are collected by UMA, do not change or reuse them.  When
+  // adding new values, do not forget to update spdyProtoPermanentValueBoundary.
+  switch (protocol) {
+    case kProtoDeprecatedSPDY2:
+      return 1;
+    case kProtoSPDY3:
+      return 2;
+    case kProtoSPDY31:
+      return 3;
+    // SPDY4 currently is HTTP/2 draft-14.
+    // TODO(bnc): increment when we update to new draft or final specification.
+    case kProtoSPDY4:
+      return 4;
+    default:
+      NOTREACHED() << "Invalid SPDY protocol.";
+      return 0;
+  }
+}
+
 NextProtoVector NextProtosHttpOnly() {
   NextProtoVector next_protos;
   next_protos.push_back(kProtoHTTP11);