Update from https://crrev.com/303153

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 <algorithm>
 
 #include "base/build_time.h"
 #include "base/logging.h"
@@ skipping 49 matching lines @@
 }
 
 }  // namespace
 
 // statics
 const int FieldTrial::kNotFinalized = -1;
 const int FieldTrial::kDefaultGroupNumber = 0;
 bool FieldTrial::enable_benchmarking_ = false;
 
 const char FieldTrialList::kPersistentStringSeparator('/');
+const char FieldTrialList::kActivationMarker('*');
 int FieldTrialList::kNoExpirationYear = 0;
 
 //------------------------------------------------------------------------------
 // FieldTrial methods and members.
 
 FieldTrial::EntropyProvider::~EntropyProvider() {
 }
 
 void FieldTrial::Disable() {
   DCHECK(!group_reported_);
@@ skipping 334 matching lines @@
   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 (name_end + 1 == group_name_end)
       return false;
     if (group_name_end == trials_string.npos)
       group_name_end = trials_string.length();
-    std::string name(trials_string, next_item, name_end - next_item);
+
+    // Verify if the trial should be activated or not.
+    std::string name;
+    bool force_activation = false;
+    if (trials_string[next_item] == kActivationMarker) {
+      // Name cannot be only the indicator.
+      if (name_end - next_item == 1)
+        return false;
+      next_item++;
+      force_activation = true;
+    }
+    name.append(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;
 
     if (ignored_trial_names.find(name) != ignored_trial_names.end())
       continue;
 
     FieldTrial* trial = CreateFieldTrial(name, group_name);
     if (!trial)
       return false;
-    if (mode == ACTIVATE_TRIALS) {
+    if (mode == ACTIVATE_TRIALS || force_activation) {
       // Call |group()| to mark the trial as "used" and notify observers, if
       // any. This is useful to ensure that field trials created in child
       // processes are properly reported in crash reports.
       trial->group();
     }
   }
   return true;
 }
 
 // static
@@ skipping 90 matching lines @@
     return;
   }
   AutoLock auto_lock(global_->lock_);
   DCHECK(!global_->PreLockedFind(trial->trial_name()));
   trial->AddRef();
   trial->SetTrialRegistered();
   global_->registered_[trial->trial_name()] = trial;
 }
 
 }  // namespace base