[chrome://flags] Let features override params in the same trial

components/flags_ui/feature_entry.h

 // 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.
 
 #ifndef COMPONENTS_FLAGS_UI_FEATURE_ENTRY_H_
 #define COMPONENTS_FLAGS_UI_FEATURE_ENTRY_H_
 
 #include <string>
 
 #include "base/strings/string16.h"
@@ skipping 129 matching lines @@
   const char* command_line_switch;
 
   // Simple switches that have no value should use "" for command_line_value.
   const char* command_line_value;
 
   // For ENABLE_DISABLE_VALUE, the command line switch and value to explicitly
   // disable the feature.
   const char* disable_command_line_switch;
   const char* disable_command_line_value;
 
-  // For FEATURE_VALUE, the base::Feature this entry corresponds to.
+  // For FEATURE_VALUE or FEATURE_WITH_VARIATIONS_VALUE, the base::Feature this
+  // entry corresponds to. The same feature must not be used in multiple
+  // FeatureEntries.
   const base::Feature* feature;
 
   // Number of options to choose from. This is used if type is MULTI_VALUE,
   // ENABLE_DISABLE_VALUE, FEATURE_VALUE, or FEATURE_WITH_VARIATIONS_VALUE.
   int num_options;
 
   // This describes the options if type is MULTI_VALUE.
   const Choice* choices;
 
   // This describes the options if type is FEATURE_WITH_VARIATIONS_VALUE.
   // The first variation is the default "Enabled" variation, its description_id
   // is disregarded.
   const FeatureVariation* feature_variations;
 
   // The name of the FieldTrial in which the selected variation parameters
-  // should be registered. This is used if type is
-  // FEATURE_WITH_VARIATIONS_VALUE.
+  // should be registered. Can be a nullptr if the parameters are accessed by
+  // their feature and the trial name is thus irrelevant. This is used if type

[Alexei Svitkine (slow), 2017/03/01 22:24:37]

This comment change should reverted now, right?

[jkrcal, 2017/03/02 08:13:12]

Done.

+  // is FEATURE_WITH_VARIATIONS_VALUE.
   const char* feature_trial_name;
 
   // Returns the name used in prefs for the option at the specified |index|.
   // Only used for types that use |num_options|.
   std::string NameForOption(int index) const;
 
   // Returns the human readable description for the option at |index|.
   // Only used for types that use |num_options|.
   base::string16 DescriptionForOption(int index) const;
 
@@ skipping 15 matching lines @@
 
 // Separator used for multi values. Multi values are represented in prefs as
 // name-of-experiment + kMultiSeparator + selected_index.
 extern const char kMultiSeparator[];
 
 }  // namespace
 
 }  // namespace flag_ui
 
 #endif  // COMPONENTS_FLAGS_UI_FEATURE_ENTRY_H_