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 203 matching lines @@
   return false;
 }
 
 void VariationsSeedProcessor::CreateTrialFromStudy(
     const ProcessedStudy& processed_study,
     const UIStringOverrideCallback& override_callback,
     const base::FieldTrial::EntropyProvider* low_entropy_provider,
     base::FeatureList* feature_list) {
   const Study& study = *processed_study.study();
 
+  // If the trial already exists, check if the selected group exists in the
+  // |processed_study|. If not, there is nothing to do here.
+  base::FieldTrial* existing_trial = base::FieldTrialList::Find(study.name());
+  if (existing_trial) {
+    int experiment_index = processed_study.GetExperimentIndexByName(
+        existing_trial->GetGroupNameWithoutActivation());
+    if (experiment_index == -1)
+      return;
+  }
+
   // Check if any experiments need to be forced due to a command line
   // flag. Force the first experiment with an existing flag.
   base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
   for (int i = 0; i < study.experiment_size(); ++i) {
     const Study_Experiment& experiment = study.experiment(i);
     if (ShouldForceExperiment(experiment, *command_line, *feature_list)) {
       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,
@@ skipping 88 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