Allow trials to associate without overriding a feature.

base/feature_list.cc

 // Copyright 2015 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/feature_list.h"
 
 #include <stddef.h>
 
 #include <utility>
 #include <vector>
@@ skipping 90 matching lines @@
 
   for (const auto& entry : overrides_) {
     std::string* target_list = nullptr;
     switch (entry.second.overridden_state) {
       case OVERRIDE_ENABLE_FEATURE:
         target_list = enable_overrides;
         break;
       case OVERRIDE_DISABLE_FEATURE:
         target_list = disable_overrides;
         break;
+      case OVERRIDE_USE_DEFAULT:
+        continue;
     }
 
     if (!target_list->empty())
       target_list->push_back(',');
     target_list->append(entry.first);
     if (entry.second.field_trial) {
       target_list->push_back('<');
       target_list->append(entry.second.field_trial->trial_name());
     }
   }
@@ skipping 49 matching lines @@
 
   auto it = overrides_.find(feature.name);
   if (it != overrides_.end()) {
     const OverrideEntry& entry = it->second;
 
     // Activate the corresponding field trial, if necessary.
     if (entry.field_trial)
       entry.field_trial->group();
 
     // TODO(asvitkine) Expand this section as more support is added.
-    return entry.overridden_state == OVERRIDE_ENABLE_FEATURE;
+
+    // If marked as OVERRIDE_USE_DEFAULT, simply return the default state below.
+    if (entry.overridden_state != OVERRIDE_USE_DEFAULT)
+      return entry.overridden_state == OVERRIDE_ENABLE_FEATURE;
   }
   // Otherwise, return the default state.
   return feature.default_state == FEATURE_ENABLED_BY_DEFAULT;
 }
 
 void FeatureList::RegisterOverridesFromCommandLine(
     const std::string& feature_list,
     OverrideState overridden_state) {
   for (const auto& value : SplitFeatureListString(feature_list)) {
     StringPiece feature_name(value);
@@ skipping 40 matching lines @@
   return it->second == &feature;
 }
 
 FeatureList::OverrideEntry::OverrideEntry(OverrideState overridden_state,
                                           FieldTrial* field_trial)
     : overridden_state(overridden_state),
       field_trial(field_trial),
       overridden_by_field_trial(field_trial != nullptr) {}
 
 }  // namespace base