Implement A/B experiment for anti-DDoS.

base/metrics/field_trial.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 "base/metrics/field_trial.h"
 
 #include "base/logging.h"
 #include "base/rand_util.h"
 #include "base/sha1.h"
 #include "base/string_util.h"
@@ skipping 351 matching lines @@
 // static
 size_t FieldTrialList::GetFieldTrialCount() {
   if (!global_)
     return 0;
   AutoLock auto_lock(global_->lock_);
   return global_->registered_.size();
 }
 
 // static
 bool FieldTrialList::IsOneTimeRandomizationEnabled() {
-  DCHECK(global_);
+  // TODO(joi): Put back a DCHECK(global_) here.  First, need to make sure all
+  // unit test executables have exactly one FieldTrialList instance (currently
+  // they have 0 or 1).
   if (!global_)
     return false;
 
   return !global_->client_id_.empty();
 }
 
 // static
 const std::string& FieldTrialList::client_id() {
   DCHECK(global_);
   if (!global_)
     return EmptyString();
 
   return global_->client_id_;
 }
 
 FieldTrial* FieldTrialList::PreLockedFind(const std::string& name) {
   RegistrationList::iterator it = registered_.find(name);
   if (registered_.end() == it)
     return NULL;
   return it->second;
 }
 
 }  // namespace base