Make --force-fieldtrials not activate them in the browser process.

base/metrics/field_trial.cc

 // Copyright (c) 2012 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 "base/metrics/field_trial.h"
 
 #include "base/build_time.h"
 #include "base/logging.h"
 #include "base/rand_util.h"
 #include "base/sha1.h"
@@ skipping 348 matching lines @@
 
   for (RegistrationList::iterator it = global_->registered_.begin();
        it != global_->registered_.end(); ++it) {
     FieldTrial::ActiveGroup active_group;
     if (it->second->GetActiveGroup(&active_group))
       active_groups->push_back(active_group);
   }
 }
 
 // static
-bool FieldTrialList::CreateTrialsFromString(const std::string& trials_string) {
+bool FieldTrialList::CreateTrialsFromString(const std::string& trials_string,
+                                            bool activate_trials) {
   DCHECK(global_);
   if (trials_string.empty() || !global_)
     return true;
 
   size_t next_item = 0;
   while (next_item < trials_string.length()) {
     size_t name_end = trials_string.find(kPersistentStringSeparator, next_item);
     if (name_end == trials_string.npos || next_item == name_end)
       return false;
     size_t group_name_end = trials_string.find(kPersistentStringSeparator,
                                                name_end + 1);
     if (group_name_end == trials_string.npos || name_end + 1 == group_name_end)
       return false;
     std::string name(trials_string, next_item, name_end - next_item);
     std::string group_name(trials_string, name_end + 1,
                            group_name_end - name_end - 1);
     next_item = group_name_end + 1;
 
     FieldTrial* trial = CreateFieldTrial(name, group_name);
     if (!trial)
       return false;
     // Call |group()| to mark the trial as "used" and notify observers, if any.
     // This is needed to ensure the trial is properly reported in child process
     // crash reports.

[Ilya Sherman, 2013/06/28 00:58:07]

nit: Please move this comment inside the if-stmt, or else tweak it to be clear
that this only happens if |activate_trials| is set (and maybe why the behavior
sometimes isn't desirable).

[Alexei Svitkine (slow), 2013/06/28 17:05:15]

Done.

-    trial->group();
+    if (activate_trials)
+      trial->group();
   }
   return true;
 }
 
 // static
 FieldTrial* FieldTrialList::CreateFieldTrial(
     const std::string& name,
     const std::string& group_name) {
   DCHECK(global_);
   DCHECK_GE(name.size(), 0u);
@@ skipping 84 matching lines @@
     used_without_global_ = true;
     return;
   }
   AutoLock auto_lock(global_->lock_);
   DCHECK(!global_->PreLockedFind(trial->trial_name()));
   trial->AddRef();
   global_->registered_[trial->trial_name()] = trial;
 }
 
 }  // namespace base