Histogram for UMA log upload connection type.

net/base/network_change_notifier.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_BASE_NETWORK_CHANGE_NOTIFIER_H_
 #define NET_BASE_NETWORK_CHANGE_NOTIFIER_H_
 
 #include <vector>
 
 #include "base/basictypes.h"
@@ skipping 23 matching lines @@
 // and will be called back on the thread from which they registered.
 // NetworkChangeNotifiers are threadsafe, though they must be created and
 // destroyed on the same thread.
 class NET_EXPORT NetworkChangeNotifier {
  public:
   // This is a superset of the connection types in the NetInfo v3 specification:
   // http://w3c.github.io/netinfo/.
   //
   // A Java counterpart will be generated for this enum.
   // GENERATED_JAVA_ENUM_PACKAGE: org.chromium.net
+  //
+  // New enum values should only be added to the end of the enum and no values
+  // should be modified or reused, as this is reported via UMA.
   enum ConnectionType {
     CONNECTION_UNKNOWN = 0,  // A connection exists, but its type is unknown.
                              // Also used as a default value.
     CONNECTION_ETHERNET = 1,
     CONNECTION_WIFI = 2,
     CONNECTION_2G = 3,
     CONNECTION_3G = 4,
     CONNECTION_4G = 5,
     CONNECTION_NONE = 6,     // No connection.
     CONNECTION_BLUETOOTH = 7,
@@ skipping 386 matching lines @@
 
   // Set true to disable non-test notifications (to prevent flakes in tests).
   bool test_notifications_only_;
 
   DISALLOW_COPY_AND_ASSIGN(NetworkChangeNotifier);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_NETWORK_CHANGE_NOTIFIER_H_