Add one-time randomization support for FieldTrial, and the ability to

net/http/http_network_transaction.cc

 // Copyright (c) 2011 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/http/http_network_transaction.h"
 
 #include <set>
 #include <vector>
 
 #include "base/compiler_specific.h"
@@ skipping 989 matching lines @@
       100);
 
   bool reused_socket = stream_->IsConnectionReused();
   if (!reused_socket) {
     UMA_HISTOGRAM_CLIPPED_TIMES(
         "Net.Transaction_Connected_New",
         total_duration,
         base::TimeDelta::FromMilliseconds(1), base::TimeDelta::FromMinutes(10),
         100);
 
-  static bool use_conn_impact_histogram(
-      base::FieldTrialList::Find("ConnCountImpact") &&
-      !base::FieldTrialList::Find("ConnCountImpact")->group_name().empty());
+  static const bool use_conn_impact_histogram =
+      base::FieldTrialList::TrialExists("ConnCountImpact");
   if (use_conn_impact_histogram) {
     UMA_HISTOGRAM_CLIPPED_TIMES(
         base::FieldTrial::MakeName("Net.Transaction_Connected_New",
             "ConnCountImpact"),
         total_duration,
         base::TimeDelta::FromMilliseconds(1), base::TimeDelta::FromMinutes(10),
         100);
     }
   }
 
-  static bool use_spdy_histogram(base::FieldTrialList::Find("SpdyImpact") &&
-      !base::FieldTrialList::Find("SpdyImpact")->group_name().empty());
+  static const bool use_spdy_histogram =
+      base::FieldTrialList::TrialExists("SpdyImpact");
   if (use_spdy_histogram && response_.was_npn_negotiated) {
     UMA_HISTOGRAM_CLIPPED_TIMES(
       base::FieldTrial::MakeName("Net.Transaction_Connected_Under_10",
                                  "SpdyImpact"),
         total_duration, base::TimeDelta::FromMilliseconds(1),
         base::TimeDelta::FromMinutes(10), 100);
 
     if (!reused_socket) {
       UMA_HISTOGRAM_CLIPPED_TIMES(
           base::FieldTrial::MakeName("Net.Transaction_Connected_New",
@@ skipping 304 matching lines @@
       description = base::StringPrintf("Unknown state 0x%08X (%u)", state,
                                        state);
       break;
   }
   return description;
 }
 
 #undef STATE_CASE
 
 }  // namespace net