Fix crash when variation parameters are set in chrome://flags.

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 257 matching lines @@
   // expiration check in field_trial.cc is based on the build date. Instead,
   // the expiration check using |reference_date| is done explicitly below.
   scoped_refptr<base::FieldTrial> trial(
       base::FieldTrialList::FactoryGetFieldTrialWithRandomizationSeed(
           study.name(), processed_study.total_probability(),
           study.default_experiment_name(),
           base::FieldTrialList::kNoExpirationYear, 1, 1, randomization_type,
           randomization_seed, NULL,
           ShouldStudyUseLowEntropy(study) ? low_entropy_provider : NULL));
 
+  // If the trial previously existed (created from command-line flags or from
+  // about:flags), the factory returns the existing trial keeping its selected
+  // group intact. If this selected group does not exist in this
+  // |processed_study|, we have nothing to do here any more.
+  const std::string& group_name = trial->group_name();

[Alexei Svitkine (slow), 2016/06/30 21:50:59]

Nit: Just inline this into the call below.

[jkrcal, 2016/07/01 10:40:54]

Done.

+  int experiment_index = processed_study.GetExperimentIndexByName(group_name);
+  if (experiment_index == -1) return;

[Alexei Svitkine (slow), 2016/06/30 21:50:59]

Nit: Put return on next line.

[jkrcal, 2016/07/01 10:40:54]

Done.

+
   bool has_overrides = false;
   bool enables_or_disables_features = 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() ||
         experiment.feature_association().has_forcing_feature_on() ||
@@ skipping 14 matching lines @@
   }
 
   trial->SetForced();
   if (processed_study.is_expired())
     trial->Disable();
 
   if (enables_or_disables_features)
     RegisterFeatureOverrides(processed_study, trial.get(), feature_list);
 
   if (study.activation_type() == Study_ActivationType_ACTIVATION_AUTO) {
-    const std::string& group_name = trial->group_name();
-
     // Don't try to apply overrides if none of the experiments in this study had
     // any.
     if (!has_overrides)
       return;
 
-    // UI Strings can only be overridden from ACTIVATION_AUTO experiments.
-    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);
-
     ApplyUIStringOverrides(study.experiment(experiment_index),
                            override_callback);
   }
 }
 
 }  // namespace variations