Add a ScopedFeatureList class for testing and start using it.

components/variations/variations_seed_processor_unittest.cc

Index: components/variations/variations_seed_processor_unittest.cc
diff --git a/components/variations/variations_seed_processor_unittest.cc b/components/variations/variations_seed_processor_unittest.cc
index 1ab8a497a38411046a4c3090e804444be1d9606b..d1e9967a2e18767b6954923593a4ad4724ad7499 100644
--- a/components/variations/variations_seed_processor_unittest.cc
+++ b/components/variations/variations_seed_processor_unittest.cc
@@ -21,6 +21,7 @@
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/test/mock_entropy_provider.h"
+#include "base/test/scoped_feature_list.h"
 #include "components/variations/processed_study.h"
 #include "components/variations/study_filtering.h"
 #include "components/variations/variations_associated_data.h"
@@ -117,8 +118,6 @@ class VariationsSeedProcessorTest : public ::testing::Test {
     // process singletons.
     testing::ClearAllVariationIDs();
     testing::ClearAllVariationParams();
-
-    base::FeatureList::ClearInstanceForTesting();
   }
 
   bool CreateTrialFromStudy(const Study& study) {
@@ -621,7 +620,6 @@ TEST_F(VariationsSeedProcessorTest, FeatureEnabledOrDisableByTrial) {
     SCOPED_TRACE(base::StringPrintf("Test[%" PRIuS "]", i));
 
     base::FieldTrialList field_trial_list(nullptr);
-    base::FeatureList::ClearInstanceForTesting();
     std::unique_ptr<base::FeatureList> feature_list(new base::FeatureList);
 
     Study study;
@@ -638,7 +636,8 @@ TEST_F(VariationsSeedProcessorTest, FeatureEnabledOrDisableByTrial) {
       association->add_disable_feature(test_case.disable_feature);
 
     EXPECT_TRUE(CreateTrialFromStudyWithFeatureList(study, feature_list.get()));
-    base::FeatureList::SetInstance(std::move(feature_list));
+    base::test::ScopedFeatureList scoped_feature_list;
+    scoped_feature_list.InitWithFeatureList(std::move(feature_list));
 
     // |kUnrelatedFeature| should not be affected.
     EXPECT_FALSE(base::FeatureList::IsEnabled(kUnrelatedFeature));
@@ -744,7 +743,6 @@ TEST_F(VariationsSeedProcessorTest, FeatureAssociationAndForcing) {
         test_case.disable_features_command_line, static_cast<int>(group)));
 
     base::FieldTrialList field_trial_list(nullptr);
-    base::FeatureList::ClearInstanceForTesting();
     std::unique_ptr<base::FeatureList> feature_list(new base::FeatureList);
     feature_list->InitializeFromCommandLine(
         test_case.enable_features_command_line,
@@ -773,7 +771,8 @@ TEST_F(VariationsSeedProcessorTest, FeatureAssociationAndForcing) {
         ->set_forcing_feature_off(test_case.feature.name);
 
     EXPECT_TRUE(CreateTrialFromStudyWithFeatureList(study, feature_list.get()));
-    base::FeatureList::SetInstance(std::move(feature_list));
+    base::test::ScopedFeatureList scoped_feature_list;
+    scoped_feature_list.InitWithFeatureList(std::move(feature_list));
 
     // Trial should not be activated initially, but later might get activated
     // depending on the expected values.
@@ -814,7 +813,6 @@ TEST_F(VariationsSeedProcessorTest, FeaturesInExpiredStudies) {
         base::StringPrintf("Test[%" PRIuS "]: %s", i, test_case.feature.name));
 
     base::FieldTrialList field_trial_list(nullptr);
-    base::FeatureList::ClearInstanceForTesting();
     std::unique_ptr<base::FeatureList> feature_list(new base::FeatureList);
     feature_list->InitializeFromCommandLine(std::string(), std::string());
 
@@ -837,7 +835,8 @@ TEST_F(VariationsSeedProcessorTest, FeaturesInExpiredStudies) {
     }
 
     EXPECT_TRUE(CreateTrialFromStudyWithFeatureList(study, feature_list.get()));
-    base::FeatureList::SetInstance(std::move(feature_list));
+    base::test::ScopedFeatureList scoped_feature_list;
+    scoped_feature_list.InitWithFeatureList(std::move(feature_list));
 
     // Tthe feature should not be enabled, because the study is expired.
     EXPECT_EQ(test_case.expected_feature_enabled,