Use low entropy for studies that send experiment IDs to Google properties.

base/metrics/field_trial.cc

 // 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.
 
 #include "base/metrics/field_trial.h"
 
 #include <algorithm>
 
 #include "base/build_time.h"
 #include "base/lazy_instance.h"
@@ skipping 363 matching lines @@
 FieldTrial* FieldTrialList::FactoryGetFieldTrial(
     const std::string& trial_name,
     FieldTrial::Probability total_probability,
     const std::string& default_group_name,
     const int year,
     const int month,
     const int day_of_month,
     FieldTrial::RandomizationType randomization_type,
     int* default_group_number) {
   return FactoryGetFieldTrialWithRandomizationSeed(
-      trial_name, total_probability, default_group_name,
-      year, month, day_of_month, randomization_type, 0, default_group_number);
+      trial_name, total_probability, default_group_name, year, month,
+      day_of_month, randomization_type, 0, default_group_number, NULL);
 }
 
 // static
 FieldTrial* FieldTrialList::FactoryGetFieldTrialWithRandomizationSeed(
     const std::string& trial_name,
     FieldTrial::Probability total_probability,
     const std::string& default_group_name,
     const int year,
     const int month,
     const int day_of_month,
     FieldTrial::RandomizationType randomization_type,
     uint32_t randomization_seed,
-    int* default_group_number) {
+    int* default_group_number,
+    const FieldTrial::EntropyProvider* override_entropy_provider) {
   if (default_group_number)
     *default_group_number = FieldTrial::kDefaultGroupNumber;
   // Check if the field trial has already been created in some other way.
   FieldTrial* existing_trial = Find(trial_name);
   if (existing_trial) {
     CHECK(existing_trial->forced_);
     // If the default group name differs between the existing forced trial
     // and this trial, then use a different value for the default group number.
     if (default_group_number &&
         default_group_name != existing_trial->default_group_name()) {
@@ skipping 13 matching lines @@
         static_assert(kNonConflictingGroupNumber != FieldTrial::kNotFinalized,
                       "The 'non-conflicting' group number conflicts");
         *default_group_number = kNonConflictingGroupNumber;
       }
     }
     return existing_trial;
   }
 
   double entropy_value;
   if (randomization_type == FieldTrial::ONE_TIME_RANDOMIZED) {
+    // If an override entropy provider is given, use it.
     const FieldTrial::EntropyProvider* entropy_provider =
-        GetEntropyProviderForOneTimeRandomization();
+        override_entropy_provider ? override_entropy_provider
+                                  : GetEntropyProviderForOneTimeRandomization();
     CHECK(entropy_provider);
     entropy_value = entropy_provider->GetEntropyForTrial(trial_name,
                                                          randomization_seed);
   } else {
     DCHECK_EQ(FieldTrial::SESSION_RANDOMIZED, randomization_type);
     DCHECK_EQ(0U, randomization_seed);
     entropy_value = RandDouble();
   }
 
   FieldTrial* field_trial = new FieldTrial(trial_name, total_probability,
@@ skipping 263 matching lines @@
     return;
   }
   AutoLock auto_lock(global_->lock_);
   CHECK(!global_->PreLockedFind(trial->trial_name())) << trial->trial_name();
   trial->AddRef();
   trial->SetTrialRegistered();
   global_->registered_[trial->trial_name()] = trial;
 }
 
 }  // namespace base