Update from chromium https://crrev.com/301315

net/base/net_log_logger.cc

 // Copyright 2013 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.
 
 #include "net/base/net_log_logger.h"
 
 #include <stdio.h>
 
 #include "base/json/json_writer.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/metrics/field_trial.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/values.h"
 #include "net/base/address_family.h"
 #include "net/base/load_states.h"
 #include "net/base/net_errors.h"
 #include "net/quic/quic_protocol.h"
 #include "net/quic/quic_utils.h"
 
 namespace {
 
@@ skipping 229 matching lines @@
 
     // Pass it as a string, since it may be too large to fit in an integer.
     constants_dict->SetString("timeTickOffset",
                               base::Int64ToString(tick_to_unix_time_ms));
   }
 
   // "clientInfo" key is required for some NetLogLogger log readers.
   // Provide a default empty value for compatibility.
   constants_dict->Set("clientInfo", new base::DictionaryValue());
 
+  // Add a list of active field experiments.
+  {
+    base::FieldTrial::ActiveGroups active_groups;
+    base::FieldTrialList::GetActiveFieldTrialGroups(&active_groups);
+    base::ListValue* field_trial_groups = new base::ListValue();
+    for (base::FieldTrial::ActiveGroups::const_iterator it =
+             active_groups.begin();
+         it != active_groups.end(); ++it) {
+      field_trial_groups->AppendString(it->trial_name + ":" +
+                                       it->group_name);
+    }
+    constants_dict->Set("activeFieldTrialGroups", field_trial_groups);
+  }
+
   return constants_dict;
 }
 
 }  // namespace net