Changes to support using base/feature_list.h from gin/.

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 <memory>
 #include <string>
@@ skipping 129 matching lines @@
   // a feature with a given name must only have a single corresponding Feature
   // struct, which is checked in builds with DCHECKs enabled.
   static bool IsEnabled(const Feature& feature);
 
   // Splits a comma-separated string containing feature names into a vector.
   static std::vector<std::string> SplitFeatureListString(
       const std::string& input);
 
   // Initializes and sets an instance of FeatureList with feature overrides via
   // command-line flags |enable_features| and |disable_features| if one has not
-  // already been set from command-line flags. No-op otherwise. See
-  // InitializeFromCommandLine for more details about |enable_features| and
-  // |disable_features| parameters.
-  static void InitializeInstance(const std::string& enable_features,
+  // already been set from command-line flags. Returns true if an instance did
+  // not previously exist. See InitializeFromCommandLine() for more details
+  // about |enable_features| and |disable_features| parameters.
+  static bool InitializeInstance(const std::string& enable_features,
                                  const std::string& disable_features);
 
   // Returns the singleton instance of FeatureList. Will return null until an
   // instance is registered via SetInstance().
   static FeatureList* GetInstance();
 
   // Registers the given |instance| to be the singleton feature list for this
   // process. This should only be called once and |instance| must not be null.
   static void SetInstance(std::unique_ptr<FeatureList> instance);
 
@@ skipping 77 matching lines @@
 
   // Whether this object has been initialized from command line.
   bool initialized_from_command_line_;
 
   DISALLOW_COPY_AND_ASSIGN(FeatureList);
 };
 
 }  // namespace base
 
 #endif  // BASE_FEATURE_LIST_H_