Allow trials to associate without overriding a feature.

base/feature_list.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 BASE_FEATURE_LIST_H_
 #define BASE_FEATURE_LIST_H_
 
 #include <map>
 #include <string>
 #include <vector>
@@ skipping 73 matching lines @@
   // enable or disable, respectively. If a feature appears on both lists, then
   // it will be disabled. If a list entry has the format "FeatureName<TrialName"
   // then this initialization will also associate the feature state override
   // with the named field trial, if it exists. Must only be invoked during the
   // initialization phase (before FinalizeInitialization() has been called).
   void InitializeFromCommandLine(const std::string& enable_features,
                                  const std::string& disable_features);
 
   // Specifies whether a feature override enables or disables the feature.
   enum OverrideState {
+    OVERRIDE_USE_DEFAULT,
     OVERRIDE_DISABLE_FEATURE,
     OVERRIDE_ENABLE_FEATURE,
   };
 
   // Returns true if the state of |feature_name| has been overridden via
   // |InitializeFromCommandLine()|.
   bool IsFeatureOverriddenFromCommandLine(const std::string& feature_name,
                                           OverrideState state) const;
 
   // Associates a field trial for reporting purposes corresponding to the
@@ skipping 125 matching lines @@
   // Whether this object has been fully initialized. This gets set to true as a
   // result of FinalizeInitialization().
   bool initialized_;
 
   DISALLOW_COPY_AND_ASSIGN(FeatureList);
 };
 
 }  // namespace base
 
 #endif  // BASE_FEATURE_LIST_H_