Do not instantiate base::FieldTrialList explicitly in tests

Recent patches introduced the initialization of FieldTrialList as part
of the test suite, hence it's no longer necessary to do so explicitly.

This patch addresses unit tests related to metrics and variations.

Bug: 1018667
Change-Id: If091b24ca3a4943841228d850c0166c14ffb3db8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1884730Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715142}

base/feature_list_unittest.cc

@@ -19,6 +19,7 @@
 #include "base/strings/string_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/test/scoped_feature_list.h"
+#include "base/test/scoped_field_trial_list_resetter.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
@@ -143,6 +144,7 @@ TEST_F(FeatureListTest, FieldTrialOverrides) {
     const auto& test_case = test_cases[i];
     SCOPED_TRACE(base::StringPrintf("Test[%" PRIuS "]", i));
 
+    test::ScopedFieldTrialListResetter resetter;
     FieldTrialList field_trial_list(nullptr);
     auto feature_list = std::make_unique<FeatureList>();
 
@@ -176,7 +178,6 @@ TEST_F(FeatureListTest, FieldTrialOverrides) {
 }
 
 TEST_F(FeatureListTest, FieldTrialAssociateUseDefault) {
-  FieldTrialList field_trial_list(nullptr);
   auto feature_list = std::make_unique<FeatureList>();
 
   FieldTrial* trial1 = FieldTrialList::CreateFieldTrial("TrialExample1", "A");
@@ -206,7 +207,6 @@ TEST_F(FeatureListTest, FieldTrialAssociateUseDefault) {
 }
 
 TEST_F(FeatureListTest, CommandLineEnableTakesPrecedenceOverFieldTrial) {
-  FieldTrialList field_trial_list(nullptr);
   auto feature_list = std::make_unique<FeatureList>();
 
   // The feature is explicitly enabled on the command-line.
@@ -229,7 +229,6 @@ TEST_F(FeatureListTest, CommandLineEnableTakesPrecedenceOverFieldTrial) {
 }
 
 TEST_F(FeatureListTest, CommandLineDisableTakesPrecedenceOverFieldTrial) {
-  FieldTrialList field_trial_list(nullptr);
   auto feature_list = std::make_unique<FeatureList>();
 
   // The feature is explicitly disabled on the command-line.
@@ -252,7 +251,6 @@ TEST_F(FeatureListTest, CommandLineDisableTakesPrecedenceOverFieldTrial) {
 }
 
 TEST_F(FeatureListTest, IsFeatureOverriddenFromCommandLine) {
-  FieldTrialList field_trial_list(nullptr);
   auto feature_list = std::make_unique<FeatureList>();
 
   // No features are overridden from the command line yet
@@ -326,6 +324,7 @@ TEST_F(FeatureListTest, AssociateReportingFieldTrial) {
                                     test_case.enable_features,
                                     test_case.disable_features));
 
+    test::ScopedFieldTrialListResetter resetter;
     FieldTrialList field_trial_list(nullptr);
     auto feature_list = std::make_unique<FeatureList>();
     feature_list->InitializeFromCommandLine(test_case.enable_features,
@@ -410,7 +409,6 @@ TEST_F(FeatureListTest, InitializeFromCommandLineThenRegisterExtraOverrides) {
 }
 
 TEST_F(FeatureListTest, GetFeatureOverrides) {
-  FieldTrialList field_trial_list(nullptr);
   auto feature_list = std::make_unique<FeatureList>();
   feature_list->InitializeFromCommandLine("A,X", "D");
 
@@ -445,7 +443,6 @@ TEST_F(FeatureListTest, GetFeatureOverrides) {
 }
 
 TEST_F(FeatureListTest, GetFeatureOverrides_UseDefault) {
-  FieldTrialList field_trial_list(nullptr);
   auto feature_list = std::make_unique<FeatureList>();
   feature_list->InitializeFromCommandLine("A,X", "D");
 
@@ -465,7 +462,6 @@ TEST_F(FeatureListTest, GetFeatureOverrides_UseDefault) {
 }
 
 TEST_F(FeatureListTest, GetFieldTrial) {
-  FieldTrialList field_trial_list(nullptr);
   FieldTrial* trial = FieldTrialList::CreateFieldTrial("Trial", "Group");
   auto feature_list = std::make_unique<FeatureList>();
   feature_list->RegisterFieldTrialOverride(
@@ -478,7 +474,6 @@ TEST_F(FeatureListTest, GetFieldTrial) {
 }
 
 TEST_F(FeatureListTest, InitializeFromCommandLine_WithFieldTrials) {
-  FieldTrialList field_trial_list(nullptr);
   FieldTrialList::CreateFieldTrial("Trial", "Group");
   auto feature_list = std::make_unique<FeatureList>();
   feature_list->InitializeFromCommandLine("A,OffByDefault<Trial,X", "D");
@@ -491,7 +486,6 @@ TEST_F(FeatureListTest, InitializeFromCommandLine_WithFieldTrials) {
 }
 
 TEST_F(FeatureListTest, InitializeFromCommandLine_UseDefault) {
-  FieldTrialList field_trial_list(nullptr);
   FieldTrialList::CreateFieldTrial("T1", "Group");
   FieldTrialList::CreateFieldTrial("T2", "Group");
   auto feature_list = std::make_unique<FeatureList>();
@@ -578,7 +572,6 @@ TEST_F(FeatureListTest, StoreAndRetrieveFeaturesFromSharedMemory) {
 }
 
 TEST_F(FeatureListTest, StoreAndRetrieveAssociatedFeaturesFromSharedMemory) {
-  FieldTrialList field_trial_list(nullptr);
   std::unique_ptr<base::FeatureList> feature_list(new base::FeatureList);
 
   // Create some overrides.

base/metrics/field_trial_params_unittest.cc

@@ -30,7 +30,7 @@ scoped_refptr<FieldTrial> CreateFieldTrial(
 
 class FieldTrialParamsTest : public ::testing::Test {
  public:
-  FieldTrialParamsTest() : field_trial_list_(nullptr) {}
+  FieldTrialParamsTest() = default;
 
   ~FieldTrialParamsTest() override {
     // Ensure that the maps are cleared between tests, since they are stored as
@@ -48,7 +48,6 @@ class FieldTrialParamsTest : public ::testing::Test {
   }
 
  private:
-  FieldTrialList field_trial_list_;
   test::ScopedFeatureList scoped_feature_list_;
 
   DISALLOW_COPY_AND_ASSIGN(FieldTrialParamsTest);

base/metrics/field_trial_unittest.cc

@@ -106,6 +106,9 @@ class FieldTrialTest : public ::testing::Test {
 
  private:
   test::TaskEnvironment task_environment_;
+  // The test suite instantiates a FieldTrialList but for the purpose of these
+  // tests it's cleaner to start from scratch.
+  test::ScopedFieldTrialListResetter trial_list_resetter_;
   FieldTrialList trial_list_;
 
   DISALLOW_COPY_AND_ASSIGN(FieldTrialTest);
@@ -1132,6 +1135,10 @@ TEST_F(FieldTrialTest, CreateSimulatedFieldTrial) {
 TEST(FieldTrialTestWithoutList, StatesStringFormat) {
   std::string save_string;
 
+  // The test suite instantiates a FieldTrialList but for the purpose of these
+  // tests it's cleaner to start from scratch.
+  test::ScopedFieldTrialListResetter trial_list_resetter_;
+
   // Scoping the first FieldTrialList, as we need another one to test the
   // importing function.
   {
@@ -1176,6 +1183,16 @@ TEST(FieldTrialDeathTest, OneTimeRandomizedTrialWithoutFieldTrialList) {
       "");
 }
 
+class FieldTrialListTest : public ::testing::Test {
+ public:
+  FieldTrialListTest() = default;
+
+ private:
+  // The test suite instantiates a FieldTrialList but for the purpose of these
+  // tests it's cleaner to start from scratch.
+  test::ScopedFieldTrialListResetter trial_list_resetter_;
+};
+
 #if defined(OS_FUCHSIA)
 // TODO(crbug.com/752368): This is flaky on Fuchsia.
 #define MAYBE_TestCopyFieldTrialStateToFlags \
@@ -1183,7 +1200,7 @@ TEST(FieldTrialDeathTest, OneTimeRandomizedTrialWithoutFieldTrialList) {
 #else
 #define MAYBE_TestCopyFieldTrialStateToFlags TestCopyFieldTrialStateToFlags
 #endif
-TEST(FieldTrialListTest, MAYBE_TestCopyFieldTrialStateToFlags) {
+TEST_F(FieldTrialListTest, MAYBE_TestCopyFieldTrialStateToFlags) {
   constexpr char kFieldTrialHandleSwitch[] = "test-field-trial-handle";
   constexpr char kEnableFeaturesSwitch[] = "test-enable-features";
   constexpr char kDisableFeaturesSwitch[] = "test-disable-features";
@@ -1213,7 +1230,7 @@ TEST(FieldTrialListTest, MAYBE_TestCopyFieldTrialStateToFlags) {
   EXPECT_EQ("C", command_line.GetSwitchValueASCII(kDisableFeaturesSwitch));
 }
 
-TEST(FieldTrialListTest, InstantiateAllocator) {
+TEST_F(FieldTrialListTest, InstantiateAllocator) {
   FieldTrialList field_trial_list(nullptr);
 
   FieldTrialList::CreateFieldTrial("Trial1", "Group1");
@@ -1230,16 +1247,14 @@ TEST(FieldTrialListTest, InstantiateAllocator) {
   EXPECT_EQ(used, new_used);
 }
 
-TEST(FieldTrialListTest, AddTrialsToAllocator) {
+TEST_F(FieldTrialListTest, AddTrialsToAllocator) {
   std::string save_string;
   base::ReadOnlySharedMemoryRegion shm_region;
 
   // Scoping the first FieldTrialList, as we need another one to test that it
   // matches.
   {
-    test::ScopedFeatureList scoped_feature_list;
-    scoped_feature_list.Init();
-
+    FieldTrialList field_trial_list1(nullptr);
     FieldTrialList::CreateFieldTrial("Trial1", "Group1");
     FieldTrialList::InstantiateFieldTrialAllocatorIfNeeded();
     FieldTrialList::AllStatesToString(&save_string, false);
@@ -1257,12 +1272,11 @@ TEST(FieldTrialListTest, AddTrialsToAllocator) {
   EXPECT_EQ(save_string, check_string);
 }
 
-TEST(FieldTrialListTest, DoNotAddSimulatedFieldTrialsToAllocator) {
+TEST_F(FieldTrialListTest, DoNotAddSimulatedFieldTrialsToAllocator) {
   constexpr char kTrialName[] = "trial";
   base::ReadOnlySharedMemoryRegion shm_region;
   {
-    test::ScopedFeatureList scoped_feature_list;
-    scoped_feature_list.Init();
+    FieldTrialList field_trial_list1(nullptr);
 
     // Create a simulated trial and a real trial and call group() on them, which
     // should only add the real trial to the field trial allocator.
@@ -1294,9 +1308,8 @@ TEST(FieldTrialListTest, DoNotAddSimulatedFieldTrialsToAllocator) {
   ASSERT_EQ(check_string.find("Simulated"), std::string::npos);
 }
 
-TEST(FieldTrialListTest, AssociateFieldTrialParams) {
-  test::ScopedFeatureList scoped_feature_list;
-  scoped_feature_list.Init();
+TEST_F(FieldTrialListTest, AssociateFieldTrialParams) {
+  FieldTrialList field_trial_list(nullptr);
 
   std::string trial_name("Trial1");
   std::string group_name("Group1");
@@ -1333,14 +1346,13 @@ TEST(FieldTrialListTest, AssociateFieldTrialParams) {
 #else
 #define MAYBE_ClearParamsFromSharedMemory ClearParamsFromSharedMemory
 #endif
-TEST(FieldTrialListTest, MAYBE_ClearParamsFromSharedMemory) {
+TEST_F(FieldTrialListTest, MAYBE_ClearParamsFromSharedMemory) {
   std::string trial_name("Trial1");
   std::string group_name("Group1");
 
   base::ReadOnlySharedMemoryRegion shm_region;
   {
-    test::ScopedFeatureList scoped_feature_list;
-    scoped_feature_list.Init();
+    FieldTrialList field_trial_list1(nullptr);
 
     // Create a field trial with some params.
     FieldTrial* trial =
@@ -1382,7 +1394,7 @@ TEST(FieldTrialListTest, MAYBE_ClearParamsFromSharedMemory) {
   EXPECT_EQ("*Trial1/Group1/", check_string);
 }
 
-TEST(FieldTrialListTest, DumpAndFetchFromSharedMemory) {
+TEST_F(FieldTrialListTest, DumpAndFetchFromSharedMemory) {
   std::string trial_name("Trial1");
   std::string group_name("Group1");
 
@@ -1459,7 +1471,7 @@ MULTIPROCESS_TEST_MAIN(SerializeSharedMemoryRegionMetadata) {
   return 0;
 }
 
-TEST(FieldTrialListTest, SerializeSharedMemoryRegionMetadata) {
+TEST_F(FieldTrialListTest, SerializeSharedMemoryRegionMetadata) {
   base::MappedReadOnlyRegion shm =
       base::ReadOnlySharedMemoryRegion::Create(4 << 10);
   ASSERT_TRUE(shm.IsValid());
@@ -1506,13 +1518,10 @@ TEST(FieldTrialListTest, SerializeSharedMemoryRegionMetadata) {
 // crbug.com/752368
 #if !defined(OS_NACL) && !defined(OS_FUCHSIA) && \
     !(defined(OS_MACOSX) && !defined(OS_IOS))
-TEST(FieldTrialListTest, CheckReadOnlySharedMemoryRegion) {
+TEST_F(FieldTrialListTest, CheckReadOnlySharedMemoryRegion) {
   FieldTrialList field_trial_list(nullptr);
   FieldTrialList::CreateFieldTrial("Trial1", "Group1");
 
-  test::ScopedFeatureList scoped_feature_list;
-  scoped_feature_list.Init();
-
   FieldTrialList::InstantiateFieldTrialAllocatorIfNeeded();
 
   base::ReadOnlySharedMemoryRegion region =

base/test/scoped_feature_list_unittest.cc

@@ -114,7 +114,6 @@ TEST_F(ScopedFeatureListTest, EnableWithFeatureParameters) {
 }
 
 TEST_F(ScopedFeatureListTest, OverrideWithFeatureParameters) {
-  FieldTrialList field_trial_list(nullptr);
   scoped_refptr<FieldTrial> trial =
       FieldTrialList::CreateFieldTrial("foo", "bar");
   const char kParam[] = "param_1";
@@ -185,7 +184,6 @@ TEST_F(ScopedFeatureListTest, OverrideWithFeatureParameters) {
 }
 
 TEST_F(ScopedFeatureListTest, OverrideMultipleFeaturesWithParameters) {
-  FieldTrialList field_trial_list(nullptr);
   scoped_refptr<FieldTrial> trial1 =
       FieldTrialList::CreateFieldTrial("foo1", "bar1");
   const char kParam[] = "param_1";
@@ -344,7 +342,6 @@ TEST_F(ScopedFeatureListTest, FeatureOverrideFeatureWithEnabledFieldTrial) {
   test::ScopedFeatureList feature_list1;
 
   std::unique_ptr<FeatureList> feature_list(new FeatureList);
-  FieldTrialList field_trial_list(nullptr);
   FieldTrial* trial = FieldTrialList::CreateFieldTrial("TrialExample", "A");
   feature_list->RegisterFieldTrialOverride(
       kTestFeature1.name, FeatureList::OVERRIDE_ENABLE_FEATURE, trial);
@@ -361,7 +358,6 @@ TEST_F(ScopedFeatureListTest, FeatureOverrideFeatureWithDisabledFieldTrial) {
   test::ScopedFeatureList feature_list1;
 
   std::unique_ptr<FeatureList> feature_list(new FeatureList);
-  FieldTrialList field_trial_list(nullptr);
   FieldTrial* trial = FieldTrialList::CreateFieldTrial("TrialExample", "A");
   feature_list->RegisterFieldTrialOverride(
       kTestFeature1.name, FeatureList::OVERRIDE_DISABLE_FEATURE, trial);

components/variations/child_process_field_trial_syncer_unittest.cc

@@ -54,7 +54,7 @@ std::pair<std::string, std::string> MakeStringPair(const std::string& a,
 
 TEST(ChildProcessFieldTrialSyncerTest, FieldTrialState) {
   base::test::SingleThreadTaskEnvironment task_environment;
-  base::FieldTrialList field_trial_list(nullptr);
+
   // We don't use the descriptor here anyways so it's ok to pass -1.
   base::FieldTrialList::CreateTrialsFromCommandLine(
       *base::CommandLine::ForCurrentProcess(), "field_trial_handle_switch", -1);

components/variations/entropy_provider_unittest.cc

@@ -17,6 +17,7 @@
 #include "base/rand_util.h"
 #include "base/stl_util.h"
 #include "base/strings/string_number_conversions.h"
+#include "base/test/scoped_field_trial_list_resetter.h"
 #include "components/variations/hashing.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -177,6 +178,7 @@ void PerformEntropyUniformityTest(
 }  // namespace
 
 TEST(EntropyProviderTest, UseOneTimeRandomizationSHA1) {
+  base::test::ScopedFieldTrialListResetter resetter;
   // Simply asserts that two trials using one-time randomization
   // that have different names, normally generate different results.
   //
@@ -206,6 +208,7 @@ TEST(EntropyProviderTest, UseOneTimeRandomizationSHA1) {
 }
 
 TEST(EntropyProviderTest, UseOneTimeRandomizationNormalizedMurmurHash) {
+  base::test::ScopedFieldTrialListResetter resetter;
   // Simply asserts that two trials using one-time randomization
   // that have different names, normally generate different results.
   //
@@ -236,6 +239,7 @@ TEST(EntropyProviderTest, UseOneTimeRandomizationNormalizedMurmurHash) {
 }
 
 TEST(EntropyProviderTest, UseOneTimeRandomizationWithCustomSeedSHA1) {
+  base::test::ScopedFieldTrialListResetter resetter;
   // Ensures that two trials with different names but the same custom seed used
   // for one time randomization produce the same group assignments.
   base::FieldTrialList field_trial_list(
@@ -263,6 +267,7 @@ TEST(EntropyProviderTest, UseOneTimeRandomizationWithCustomSeedSHA1) {
 
 TEST(EntropyProviderTest,
      UseOneTimeRandomizationWithCustomSeedNormalizedMurmurHash) {
+  base::test::ScopedFieldTrialListResetter resetter;
   // Ensures that two trials with different names but the same custom seed used
   // for one time randomization produce the same group assignments.
   base::FieldTrialList field_trial_list(

components/variations/field_trial_config/field_trial_util_unittest.cc

@@ -52,7 +52,7 @@ class TestOverrideStringCallback {
 
 class FieldTrialUtilTest : public ::testing::Test {
  public:
-  FieldTrialUtilTest() : field_trial_list_(nullptr) {}
+  FieldTrialUtilTest() {}
 
   ~FieldTrialUtilTest() override {
     // Ensure that the maps are cleared between tests, since they are stored as
@@ -75,7 +75,6 @@ class FieldTrialUtilTest : public ::testing::Test {
   }
 
  protected:
-  base::FieldTrialList field_trial_list_;
   TestOverrideStringCallback override_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(FieldTrialUtilTest);

components/variations/net/variations_command_line_unittest.cc

@@ -21,7 +21,6 @@ TEST(VariationsCommandLineTest, TestGetVariationsCommandLine) {
   std::string enable_feature_list = "feature1<trial1";
   std::string disable_feature_list = "feature2<trial2";
 
-  base::FieldTrialList field_trial_list(nullptr);
   AssociateParamsFromString(param_list);
   base::FieldTrialList::CreateTrialsFromString(trial_list,
                                                std::set<std::string>());
@@ -36,4 +35,4 @@ TEST(VariationsCommandLineTest, TestGetVariationsCommandLine) {
   EXPECT_NE(output.find(disable_feature_list), std::string::npos);
 }
 
-}  // namespace variations
+}  // namespace variations
\ No newline at end of file

components/variations/service/variations_field_trial_creator_unittest.cc

@@ -268,7 +268,7 @@ class TestVariationsFieldTrialCreator : public VariationsFieldTrialCreator {
 
 class FieldTrialCreatorTest : public ::testing::Test {
  protected:
-  FieldTrialCreatorTest() : field_trial_list_(nullptr) {
+  FieldTrialCreatorTest() {
     VariationsService::RegisterPrefs(prefs_.registry());
     global_feature_list_ = base::FeatureList::ClearInstanceForTesting();
   }
@@ -288,9 +288,6 @@ class FieldTrialCreatorTest : public ::testing::Test {
   // The global feature list, which is ignored by tests in this suite.
   std::unique_ptr<base::FeatureList> global_feature_list_;
 
-  // A local FieldTrialList to hold any field trials created in this suite.
-  base::FieldTrialList field_trial_list_;
-
   DISALLOW_COPY_AND_ASSIGN(FieldTrialCreatorTest);
 };
 

components/variations/synthetic_trial_registry_unittest.cc

@@ -21,7 +21,7 @@ namespace {
 
 class SyntheticTrialRegistryTest : public ::testing::Test {
  public:
-  SyntheticTrialRegistryTest() : field_trial_list_(nullptr) { InitCrashKeys(); }
+  SyntheticTrialRegistryTest() { InitCrashKeys(); }
   ~SyntheticTrialRegistryTest() override { ClearCrashKeysInstanceForTesting(); }
 
   // Returns true if there is a synthetic trial in the given vector that matches
@@ -49,8 +49,6 @@ class SyntheticTrialRegistryTest : public ::testing::Test {
  private:
   base::test::SingleThreadTaskEnvironment task_environment_;
 
-  base::FieldTrialList field_trial_list_;
-
   DISALLOW_COPY_AND_ASSIGN(SyntheticTrialRegistryTest);
 };
 

components/variations/variations_associated_data_unittest.cc

@@ -36,7 +36,7 @@ scoped_refptr<base::FieldTrial> CreateFieldTrial(
 
 class VariationsAssociatedDataTest : public ::testing::Test {
  public:
-  VariationsAssociatedDataTest() : field_trial_list_(nullptr) {}
+  VariationsAssociatedDataTest() {}
 
   ~VariationsAssociatedDataTest() override {
     // Ensure that the maps are cleared between tests, since they are stored as
@@ -45,8 +45,6 @@ class VariationsAssociatedDataTest : public ::testing::Test {
   }
 
  private:
-  base::FieldTrialList field_trial_list_;
-
   DISALLOW_COPY_AND_ASSIGN(VariationsAssociatedDataTest);
 };
 

components/variations/variations_crash_keys_unittest.cc

@@ -30,7 +30,7 @@ std::string GetNumExperimentsCrashKey() {
 
 class VariationsCrashKeysTest : public ::testing::Test {
  public:
-  VariationsCrashKeysTest() : field_trial_list_(nullptr) {
+  VariationsCrashKeysTest() {
     crash_reporter::ResetCrashKeysForTesting();
     crash_reporter::InitializeCrashKeysForTesting();
   }
@@ -44,8 +44,6 @@ class VariationsCrashKeysTest : public ::testing::Test {
  private:
   base::test::SingleThreadTaskEnvironment task_environment_;
 
-  base::FieldTrialList field_trial_list_;
-
   DISALLOW_COPY_AND_ASSIGN(VariationsCrashKeysTest);
 };
 

components/variations/variations_http_header_provider_unittest.cc

@@ -43,8 +43,12 @@ scoped_refptr<base::FieldTrial> CreateTrialAndAssociateId(
     VariationID id) {
   scoped_refptr<base::FieldTrial> trial(
       base::FieldTrialList::CreateFieldTrial(trial_name, default_group_name));
+  EXPECT_TRUE(trial);
 
-  AssociateGoogleVariationID(key, trial->trial_name(), trial->group_name(), id);
+  if (trial) {
+    AssociateGoogleVariationID(key, trial->trial_name(), trial->group_name(),
+                               id);
+  }
 
   return trial;
 }
@@ -123,7 +127,6 @@ TEST_F(VariationsHttpHeaderProviderTest, ForceVariationIds_Invalid) {
 
 TEST_F(VariationsHttpHeaderProviderTest, OnFieldTrialGroupFinalized) {
   base::test::SingleThreadTaskEnvironment task_environment;
-  base::FieldTrialList field_trial_list(nullptr);
   VariationsHttpHeaderProvider provider;
   provider.InitVariationIDsCacheIfNeeded();
 
@@ -172,7 +175,6 @@ TEST_F(VariationsHttpHeaderProviderTest, OnFieldTrialGroupFinalized) {
 
 TEST_F(VariationsHttpHeaderProviderTest, GetVariationsString) {
   base::test::SingleThreadTaskEnvironment task_environment;
-  base::FieldTrialList field_trial_list(nullptr);
 
   CreateTrialAndAssociateId("t1", "g1", GOOGLE_WEB_PROPERTIES, 123);
   CreateTrialAndAssociateId("t2", "g2", GOOGLE_WEB_PROPERTIES, 124);
@@ -186,8 +188,6 @@ TEST_F(VariationsHttpHeaderProviderTest, GetVariationsString) {
 
 TEST_F(VariationsHttpHeaderProviderTest, GetVariationsVector) {
   base::test::SingleThreadTaskEnvironment task_environment;
-  base::FieldTrialList field_trial_list(nullptr);
-
   CreateTrialAndAssociateId("t1", "g1", GOOGLE_WEB_PROPERTIES, 121);
   CreateTrialAndAssociateId("t2", "g2", GOOGLE_WEB_PROPERTIES, 122);
   CreateTrialAndAssociateId("t3", "g3", GOOGLE_WEB_PROPERTIES_TRIGGER, 123);

components/variations/variations_id_collection_unittest.cc

@@ -8,7 +8,6 @@
 #include <vector>
 
 #include "base/bind.h"
-#include "base/metrics/field_trial.h"
 #include "base/run_loop.h"
 #include "base/test/task_environment.h"
 #include "components/variations/variations_associated_data.h"
@@ -57,7 +56,7 @@ void SetupAndFinalizeTrial(const std::string& trial_name,
 
 class VariationsIdCollectionTest : public ::testing::Test {
  public:
-  VariationsIdCollectionTest() : field_trial_list_(nullptr) {}
+  VariationsIdCollectionTest() {}
 
   ~VariationsIdCollectionTest() override { testing::ClearAllVariationIDs(); }
 
@@ -75,7 +74,6 @@ class VariationsIdCollectionTest : public ::testing::Test {
 
  private:
   base::test::SingleThreadTaskEnvironment task_environment_;
-  base::FieldTrialList field_trial_list_;
   std::unique_ptr<VariationsIdCollection> collection_;
   std::vector<VariationID> new_ids_;
 };

components/variations/variations_params_manager.h

@@ -11,6 +11,7 @@
 #include <string>
 
 #include "base/macros.h"
+#include "base/test/scoped_field_trial_list_resetter.h"
 
 namespace base {
 class CommandLine;
@@ -88,6 +89,7 @@ class VariationParamsManager {
       base::CommandLine* command_line);
 
  private:
+  base::test::ScopedFieldTrialListResetter field_trial_list_resetter_;
   std::unique_ptr<base::FieldTrialList> field_trial_list_;
   std::unique_ptr<base::test::ScopedFeatureList> scoped_feature_list_;
 

components/variations/variations_seed_simulator_unittest.cc

@@ -71,7 +71,7 @@ Study_Experiment_Param* AddExperimentParam(const std::string& param_name,
 
 class VariationsSeedSimulatorTest : public ::testing::Test {
  public:
-  VariationsSeedSimulatorTest() : field_trial_list_(nullptr) {}
+  VariationsSeedSimulatorTest() {}
 
   ~VariationsSeedSimulatorTest() override {
     // Ensure that the maps are cleared between tests, since they are stored as
@@ -128,8 +128,6 @@ class VariationsSeedSimulatorTest : public ::testing::Test {
   }
 
  private:
-  base::FieldTrialList field_trial_list_;
-
   DISALLOW_COPY_AND_ASSIGN(VariationsSeedSimulatorTest);
 };