Allow trials to associate without overriding a feature.

components/variations/variations_seed_processor.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 "components/variations/variations_seed_processor.h"
 
 #include <stddef.h>
 
 #include <map>
 #include <vector>
@@ skipping 89 matching lines @@
 // Registers feature overrides for the chosen experiment in the specified study.
 void RegisterFeatureOverrides(const ProcessedStudy& processed_study,
                               base::FieldTrial* trial,
                               base::FeatureList* feature_list) {
   const std::string& group_name = trial->GetGroupNameWithoutActivation();
   int experiment_index = processed_study.GetExperimentIndexByName(group_name);
   // The field trial was defined from |study|, so the active experiment's name
   // must be in the |study|.
   DCHECK_NE(-1, experiment_index);
 
-  const Study_Experiment& experiment =
-      processed_study.study()->experiment(experiment_index);
+  const Study& study = *processed_study.study();
+  const Study_Experiment& experiment = study.experiment(experiment_index);
 
   // Process all the features to enable.
   int feature_count = experiment.feature_association().enable_feature_size();
   for (int i = 0; i < feature_count; ++i) {
     feature_list->RegisterFieldTrialOverride(
         experiment.feature_association().enable_feature(i),
         base::FeatureList::OVERRIDE_ENABLE_FEATURE, trial);
   }
 
   // Process all the features to disable.
   feature_count = experiment.feature_association().disable_feature_size();
   for (int i = 0; i < feature_count; ++i) {
     feature_list->RegisterFieldTrialOverride(
         experiment.feature_association().disable_feature(i),
         base::FeatureList::OVERRIDE_DISABLE_FEATURE, trial);
   }
+
+  // Check if this study enables/disables a single feature and uses explicit
+  // activation (i.e. the trial should be activated when queried). If so, ensure
+  // that groups that don't explicitly enable/disable that feature are still
+  // associated with it (i.e. so "Default" group gets reported).
+  //
+  // Note: This checks for ACTIVATION_EXPLICIT, since there is no reason to
+  // have this association with ACTIVATION_AUTO (where the trial starts active),
+  // as well as allowing flexibility to disable this behavior in the future from
+  // the server by introducing a new activation type.
+  if (!processed_study.single_feature_name().empty() &&
+      study.activation_type() == Study_ActivationType_ACTIVATION_EXPLICIT &&
+      !experiment.has_feature_association()) {
+    feature_list->RegisterFieldTrialOverride(
+        processed_study.single_feature_name(),
+        base::FeatureList::OVERRIDE_USE_DEFAULT, trial);
+  }
 }
 
 // Checks if |experiment| is associated with a forcing flag or feature and if it
 // is, returns whether it should be forced enabled based on the |command_line|
 // or |feature_list| state.
 bool ShouldForceExperiment(const Study_Experiment& experiment,
                            const base::CommandLine& command_line,
                            const base::FeatureList& feature_list) {
   if (experiment.feature_association().has_forcing_feature_on()) {
     return feature_list.IsFeatureOverriddenFromCommandLine(
@@ skipping 146 matching lines @@
     // The field trial was defined from |study|, so the active experiment's name
     // must be in the |study|.
     DCHECK_NE(-1, experiment_index);
 
     ApplyUIStringOverrides(study.experiment(experiment_index),
                            override_callback);
   }
 }
 
 }  // namespace variations