Fix crash with forcing variations when the trial exists.

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 <map>
 #include <vector>
 
 #include "base/command_line.h"
@@ skipping 93 matching lines @@
   // Check if any experiments need to be forced due to a command line
   // flag. Force the first experiment with an existing flag.
   CommandLine* command_line = CommandLine::ForCurrentProcess();
   for (int i = 0; i < study.experiment_size(); ++i) {
     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
+      // 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)
+        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);
       }
 
       DVLOG(1) << "Trial " << study.name() << " forced by flag: "
                << experiment.forcing_flag();
@@ skipping 56 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