Add a ScopedFeatureList class for testing and start using it.

base/test/scoped_feature_list.cc

+// 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.
+
+#include "base/test/scoped_feature_list.h"
+
+namespace base {
+namespace test {
+
+ScopedFeatureList::ScopedFeatureList() {}
+
+ScopedFeatureList::~ScopedFeatureList() {
+  if (original_feature_list_) {
+    base::FeatureList::ClearInstanceForTesting();
+    base::FeatureList::RestoreInstanceForTesting(
+        std::move(original_feature_list_));
+  }
+}
+
+void ScopedFeatureList::Init() {
+  std::unique_ptr<base::FeatureList> feature_list(new base::FeatureList);
+  feature_list->InitializeFromCommandLine(std::string(), std::string());
+  InitWithFeatureList(std::move(feature_list));
+}
+
+void ScopedFeatureList::InitWithFeatureList(
+    std::unique_ptr<FeatureList> feature_list) {
+  DCHECK(!original_feature_list_);
+  original_feature_list_ = base::FeatureList::ClearInstanceForTesting();
+  base::FeatureList::SetInstance(std::move(feature_list));
+}
+
+void ScopedFeatureList::InitFromCommandLine(
+    const std::string& enable_features,
+    const std::string& disable_features) {
+  std::unique_ptr<base::FeatureList> feature_list(new base::FeatureList);
+  feature_list->InitializeFromCommandLine(enable_features, disable_features);
+  InitWithFeatureList(std::move(feature_list));
+}
+
+void ScopedFeatureList::InitAndEnableFeature(const base::Feature& feature) {
+  InitFromCommandLine(feature.name, std::string());
+}
+
+void ScopedFeatureList::InitAndDisableFeature(const base::Feature& feature) {
+  InitFromCommandLine(std::string(), feature.name);
+}
+
+}  // namespace test
+}  // namespace base