Expand FeatureList to support FieldTrial association.

components/variations/variations_seed_processor.cc

Index: components/variations/variations_seed_processor.cc
diff --git a/components/variations/variations_seed_processor.cc b/components/variations/variations_seed_processor.cc
index 169ac63104b2e983b778fe00b9de0a3fa26630fb..d12cb49277526409ac9bf663ca2bca2c5b4557c9 100644
--- a/components/variations/variations_seed_processor.cc
+++ b/components/variations/variations_seed_processor.cc
@@ -8,6 +8,7 @@
 #include <vector>
 
 #include "base/command_line.h"
+#include "base/feature_list.h"
 #include "base/metrics/field_trial.h"
 #include "base/strings/utf_string_conversions.h"
 #include "components/variations/processed_study.h"
@@ -79,6 +80,21 @@ void ApplyUIStringOverrides(
   }
 }
 
+// Forces the specified |experiment| to be enabled in |study|.
+void ForceExperimentState(
+    const Study& study,
+    const Study_Experiment& experiment,
+    const VariationsSeedProcessor::UIStringOverrideCallback& override_callback,
+    base::FieldTrial* trial) {
+  RegisterExperimentParams(study, experiment);
+  RegisterVariationIds(experiment, study.name());
+  if (study.activation_type() == Study_ActivationType_ACTIVATION_AUTO) {
+    trial->group();
+    // UI Strings can only be overridden from ACTIVATION_AUTO experiments.
+    ApplyUIStringOverrides(experiment, override_callback);
+  }
+}
+
 }  // namespace
 
 VariationsSeedProcessor::VariationsSeedProcessor() {
@@ -97,7 +113,8 @@ void VariationsSeedProcessor::CreateTrialsFromSeed(
     const std::string& hardware_class,
     const std::string& session_consistency_country,
     const std::string& permanent_consistency_country,
-    const UIStringOverrideCallback& override_callback) {
+    const UIStringOverrideCallback& override_callback,
+    base::FeatureList* feature_list) {
   std::vector<ProcessedStudy> filtered_studies;
   FilterAndValidateStudies(seed, locale, reference_date, version, channel,
                            form_factor, hardware_class,
@@ -105,12 +122,13 @@ void VariationsSeedProcessor::CreateTrialsFromSeed(
                            permanent_consistency_country, &filtered_studies);
 
   for (size_t i = 0; i < filtered_studies.size(); ++i)
-    CreateTrialFromStudy(filtered_studies[i], override_callback);
+    CreateTrialFromStudy(filtered_studies[i], override_callback, feature_list);
 }
 
 void VariationsSeedProcessor::CreateTrialFromStudy(
     const ProcessedStudy& processed_study,
-    const UIStringOverrideCallback& override_callback) {
+    const UIStringOverrideCallback& override_callback,
+    base::FeatureList* feature_list) {
   const Study& study = *processed_study.study();
 
   // Check if any experiments need to be forced due to a command line
@@ -120,28 +138,43 @@ void VariationsSeedProcessor::CreateTrialFromStudy(
     const Study_Experiment& experiment = study.experiment(i);
     if (experiment.has_forcing_flag() &&
         command_line->HasSwitch(experiment.forcing_flag())) {
-      scoped_refptr<base::FieldTrial> trial(
-          base::FieldTrialList::CreateFieldTrial(study.name(),
-                                                 experiment.name()));
-      // If |trial| is NULL, then there might already be a trial forced to a
+      base::FieldTrial* trial = base::FieldTrialList::CreateFieldTrial(
+          study.name(), experiment.name());
+      // If |trial| is null, then there might already be a trial forced to a
       // different group (e.g. via --force-fieldtrials). Break out of the loop,
       // but don't return, so that variation ids and params for the selected
       // group will still be picked up.
-      if (!trial.get())
+      if (!trial)
         break;
 
-      RegisterExperimentParams(study, experiment);
-      RegisterVariationIds(experiment, study.name());
-      if (study.activation_type() == Study_ActivationType_ACTIVATION_AUTO) {
-        trial->group();
-        // UI Strings can only be overridden from ACTIVATION_AUTO experiments.
-        ApplyUIStringOverrides(experiment, override_callback);
-      }
-
+      ForceExperimentState(study, experiment, override_callback, trial);
       DVLOG(1) << "Trial " << study.name() << " forced by flag: "
                << experiment.forcing_flag();
       return;
     }
+
+    base::FieldTrial* trial;
+    if (experiment.feature_association().has_forcing_feature_on()) {
+      trial = feature_list->AssociateReportingFieldTrial(
+          experiment.feature_association().forcing_feature_on(),
+          base::FeatureList::OVERRIDE_ENABLE_FEATURE, study.name(),
+          experiment.name());
+    } else if (experiment.feature_association().has_forcing_feature_off()) {
+      trial = feature_list->AssociateReportingFieldTrial(
+          experiment.feature_association().forcing_feature_off(),
+          base::FeatureList::OVERRIDE_DISABLE_FEATURE, study.name(),
+          experiment.name());
+    } else {
+      continue;
+    }
+
+    // If |trial| is null, then the specified feature has not been forced on or
+    // off on the FeatureList via the command-line, so safe to skip this entry.
+    if (trial) {
+      // Otherwise, force this experiment state and we're done with this study.
+      ForceExperimentState(study, experiment, override_callback, trial);
+      return;
+    }
   }
 
   uint32 randomization_seed = 0;
@@ -169,14 +202,18 @@ void VariationsSeedProcessor::CreateTrialFromStudy(
           randomization_seed, NULL));
 
   bool has_overrides = false;
+  bool controls_feature_state = false;
   for (int i = 0; i < study.experiment_size(); ++i) {
     const Study_Experiment& experiment = study.experiment(i);
     RegisterExperimentParams(study, experiment);
 
     // Groups with forcing flags have probability 0 and will never be selected.
     // Therefore, there's no need to add them to the field trial.
-    if (experiment.has_forcing_flag())
+    if (experiment.has_forcing_flag() ||
+        experiment.feature_association().has_forcing_feature_on() ||
+        experiment.feature_association().has_forcing_feature_off()) {
       continue;
+    }
 
     if (experiment.name() != study.default_experiment_name())
       trial->AppendGroup(experiment.name(), experiment.probability_weight());
@@ -184,9 +221,35 @@ void VariationsSeedProcessor::CreateTrialFromStudy(
     RegisterVariationIds(experiment, study.name());
 
     has_overrides = has_overrides || experiment.override_ui_string_size() > 0;
+    if (experiment.feature_association().enable_feature_size() != 0 ||
+        experiment.feature_association().disable_feature_size() != 0) {
+      controls_feature_state = true;
+    }
   }
-
   trial->SetForced();
+
+  if (controls_feature_state) {
+    const std::string& group_name = trial->GetGroupNameWithoutActivation();

[rkaplow, 2015/09/14 21:20:12]

this method is getting a bit unwieldly - I think you can pull this part into a
seperate method

[Alexei Svitkine (slow), 2015/09/14 22:03:44]

Done.

+    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 = study.experiment(experiment_index);
+    int feature_count = experiment.feature_association().enable_feature_size();

[rkaplow, 2015/09/14 21:20:12]

I'd comment on this and the follow block

[Alexei Svitkine (slow), 2015/09/14 22:03:44]

Done.

+    for (int i = 0; i < feature_count; ++i) {
+      feature_list->RegisterFieldTrialOverride(
+          experiment.feature_association().enable_feature(i),
+          base::FeatureList::OVERRIDE_ENABLE_FEATURE, trial.get());
+    }
+    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.get());
+    }
+  }
+
   if (processed_study.is_expired()) {
     trial->Disable();
   } else if (study.activation_type() == Study_ActivationType_ACTIVATION_AUTO) {