Introduce new SPDY Version UMA histogram.

net/socket/next_proto.h

 // Copyright (c) 2012 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_SOCKET_NEXT_PROTO_H_
 #define NET_SOCKET_NEXT_PROTO_H_
 
 #include <vector>
 
 #include "net/base/net_export.h"
@@ skipping 14 matching lines @@
   kProtoSPDY3,
   kProtoSPDY31,
   kProtoSPDY4,  // SPDY4 is HTTP/2.
   kProtoSPDYMaximumVersion = kProtoSPDY4,
 
   kProtoQUIC1SPDY3,
 
   kProtoMaximumVersion = kProtoQUIC1SPDY3,
 };
 
+// NextProto is contiguous, therefore values can change when protocols are
+// removed.  This function returns invariant values, so that UMA histograms can
+// be combined for different releases.
+unsigned int SpdyProtoPermanentValue(NextProto protocol);
+
+// One larger than the maximum value SpdyProtoPermanentValue can return.
+const unsigned int spdyProtoPermanentValueBoundary = 5;

[Alexei Svitkine (slow), 2014/09/11 18:29:58]

I suggest just making an enum for the PermanentValue version of these values,
then this can be part of the enum and the return value of the function can also
be the enum, so we get type safety (and no chance for someone to accidentally
add a new value but forget to update this).

[Bence, 2014/09/12 12:37:07]

You're right, we need a proper enum here.

This is getting very complicated.  I would in fact prefer to make the values in
NextProto permanent, eliminating the need for an extra enum.    NextProto being
noncontiguous only breaks a single for cycle:
https://code.google.com/p/chromium/codesearch#chromium/src/net/spdy/spdy_test....
 I would prefer to replace that by spelling out every protocol, like in
https://code.google.com/p/chromium/codesearch#chromium/src/net/socket/next_pr....
 This would also eliminate the need for a translating function, so overall
maintenance would be easier.

[Alexei Svitkine (slow), 2014/09/12 14:38:08]

That SGTM.

[Bence, 2014/09/12 20:16:56]

Done.

+
 // List of protocols to use for NPN, used for configuring HttpNetworkSessions.
 typedef std::vector<NextProto> NextProtoVector;
 
 // Convenience functions to create NextProtoVector.
 
 NET_EXPORT NextProtoVector NextProtosHttpOnly();
 
 // Default values, which are subject to change over time.  Currently just
 // SPDY 3 and 3.1.
 NET_EXPORT NextProtoVector NextProtosDefaults();
 
 NET_EXPORT NextProtoVector NextProtosWithSpdyAndQuic(bool spdy_enabled,
                                                      bool quic_enabled);
 
 // All of these also enable QUIC.
 NET_EXPORT NextProtoVector NextProtosSpdy3();
 NET_EXPORT NextProtoVector NextProtosSpdy31();
 NET_EXPORT NextProtoVector NextProtosSpdy31WithSpdy2();
 NET_EXPORT NextProtoVector NextProtosSpdy4Http2();
 
 }  // namespace net
 
 #endif  // NET_SOCKET_NEXT_PROTO_H_