Reland of Change ScopedFeatureList to overrides FeatureList not reset

base/test/scoped_feature_list.h

 // Copyright 2016 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_TEST_SCOPED_FEATURE_LIST_H_
 #define BASE_TEST_SCOPED_FEATURE_LIST_H_
 
 #include <initializer_list>
 
 #include "base/feature_list.h"
@@ skipping 14 matching lines @@
 //   overriden ::testing::Test::SetUp method. For example:
 //     void SetUp() override {
 //       scoped_feature_list_.InitAndEnableFeature(features::kMyFeatureHere);
 //       InProcessBrowserTest::SetUp();
 //     }
 class ScopedFeatureList final {
  public:
   ScopedFeatureList();
   ~ScopedFeatureList();
 
+  // WARNING: This method will reset any globally configured features to their
+  // default values, which can hide feature interaction bugs. Please use
+  // sparingly.  https://crbug.com/713390
   // Initializes and registers a FeatureList instance with no overrides.
   void Init();
 
+  // WARNING: This method will reset any globally configured features to their
+  // default values, which can hide feature interaction bugs. Please use
+  // sparingly.  https://crbug.com/713390
   // Initializes and registers the given FeatureList instance.
   void InitWithFeatureList(std::unique_ptr<FeatureList> feature_list);
 
-  // Initializes and registers a FeatureList instance with the given enabled
-  // and disabled features.
+  // WARNING: This method will reset any globally configured features to their
+  // default values, which can hide feature interaction bugs. Please use
+  // sparingly.  https://crbug.com/713390
+  // Initializes and registers a FeatureList instance with only the given
+  // enabled and disabled features (comma-separated names).
+  void InitFromCommandLine(const std::string& enable_features,
+                           const std::string& disable_features);
+
+  // Initializes and registers a FeatureList instance based on present
+  // FeatureList and overridden with the given enabled and disabled features.
+  // Any feature overrides already present in the global FeatureList will
+  // continue to apply, unless they conflict with the overrides passed into this
+  // method. This is important for testing potentially unexpected feature
+  // interactions.
   void InitWithFeatures(
       const std::initializer_list<base::Feature>& enabled_features,
       const std::initializer_list<base::Feature>& disabled_features);
 
-  // Initializes and registers a FeatureList instance with the given
-  // enabled and disabled features (comma-separated names).
-  void InitFromCommandLine(const std::string& enable_features,
-                           const std::string& disable_features);
-
-  // Initializes and registers a FeatureList instance enabling a single
-  // feature.
+  // Initializes and registers a FeatureList instance based on present
+  // FeatureList and overridden with single enabled feature.
   void InitAndEnableFeature(const base::Feature& feature);
 
-  // Initializes and registers a FeatureList instance disabling a single
-  // feature.
+  // Initializes and registers a FeatureList instance based on present
+  // FeatureList and overridden with single disabled feature.
   void InitAndDisableFeature(const base::Feature& feature);
 
  private:
   std::unique_ptr<FeatureList> original_feature_list_;
 
   DISALLOW_COPY_AND_ASSIGN(ScopedFeatureList);
 };
 
 }  // namespace test
 }  // namespace base
 
 #endif  // BASE_TEST_SCOPED_FEATURE_LIST_H_