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

net/http/http_cache_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_cache_transaction.h"
 
 #include "build/build_config.h"
 
 #if defined(OS_POSIX)
 #include <unistd.h>
@@ skipping 847 matching lines @@
 }
 
 int HttpCache::Transaction::DoAddToEntryComplete(int result) {
   net_log_.EndEventWithNetErrorCode(NetLog::TYPE_HTTP_CACHE_ADD_TO_ENTRY,
                                     result);
 
   const base::TimeDelta entry_lock_wait =
       base::TimeTicks::Now() - entry_lock_waiting_since_;
   UMA_HISTOGRAM_TIMES("HttpCache.EntryLockWait", entry_lock_wait);
   static const bool prefetching_fieldtrial =
-      base::FieldTrialList::Find("Prefetch") &&
-      !base::FieldTrialList::Find("Prefetch")->group_name().empty();
+      base::FieldTrialList::TrialExists("Prefetch");
   if (prefetching_fieldtrial) {
     UMA_HISTOGRAM_TIMES(
         base::FieldTrial::MakeName("HttpCache.EntryLockWait", "Prefetch"),
         entry_lock_wait);
   }
 
   entry_lock_waiting_since_ = base::TimeTicks();
   DCHECK(new_entry_);
   cache_pending_ = false;
 
@@ skipping 1120 matching lines @@
     return false;
 
   return true;
 }
 
 void HttpCache::Transaction::OnIOComplete(int result) {
   DoLoop(result);
 }
 
 }  // namespace net