Do not instantiate base::FieldTrialList explicitly in tests

The test suite already instantiates a FieldTrialList as per
https://chromium-review.googlesource.com/c/chromium/src/+/1883567 so
it's no longer necessary to do so explicitly in tests.

This patch addresses unit tests under:
/components/omnibox

This CL was uploaded by git cl split.

R=mpearson@chromium.org

Bug: 1018667
Change-Id: Idb0b248873001282c98db87a6dfc6381d45bbbc0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1917229
Commit-Queue: Mikel Astiz <mastiz@chromium.org>
Reviewed-by: Justin Donnelly <jdonnelly@chromium.org>
Auto-Submit: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#716144}

components/omnibox/browser/autocomplete_result_unittest.cc

@@ -30,7 +30,6 @@
 #include "components/omnibox/browser/test_scheme_classifier.h"
 #include "components/omnibox/common/omnibox_features.h"
 #include "components/search_engines/template_url_service.h"
-#include "components/variations/entropy_provider.h"
 #include "components/variations/variations_associated_data.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -113,11 +112,6 @@ class AutocompleteResultTest : public testing::Test {
   };
 
   AutocompleteResultTest() {
-    // Destroy the existing FieldTrialList before creating a new one to avoid
-    // a DCHECK.
-    field_trial_list_.reset();
-    field_trial_list_.reset(new base::FieldTrialList(
-        std::make_unique<variations::SHA1EntropyProvider>("foo")));
     variations::testing::ClearAllVariationParams();
 
     // Create the list of mock providers.  5 is enough.
@@ -168,7 +162,6 @@ class AutocompleteResultTest : public testing::Test {
 
  private:
   base::test::TaskEnvironment task_environment_;
-  std::unique_ptr<base::FieldTrialList> field_trial_list_;
 
   // For every provider mentioned in TestData, we need a mock provider.
   std::vector<scoped_refptr<MockAutocompleteProvider> > mock_provider_list_;

components/omnibox/browser/document_suggestions_service_unittest.cc

@@ -42,7 +42,6 @@ class DocumentSuggestionsServiceTest : public testing::Test {
             base::MakeRefCounted<network::WeakWrapperSharedURLLoaderFactory>(
                 &test_url_loader_factory_)),
         identity_test_env_(&test_url_loader_factory_, &prefs_),
-        field_trial_list_(nullptr),
         document_suggestions_service_(new DocumentSuggestionsService(
             identity_test_env_.identity_manager(),
             shared_url_loader_factory_)) {
@@ -64,7 +63,6 @@ class DocumentSuggestionsServiceTest : public testing::Test {
   scoped_refptr<network::SharedURLLoaderFactory> shared_url_loader_factory_;
   sync_preferences::TestingPrefServiceSyncable prefs_;
   signin::IdentityTestEnvironment identity_test_env_;
-  base::FieldTrialList field_trial_list_;
   std::unique_ptr<DocumentSuggestionsService> document_suggestions_service_;
 
   DISALLOW_COPY_AND_ASSIGN(DocumentSuggestionsServiceTest);

components/omnibox/browser/keyword_provider_unittest.cc

@@ -23,7 +23,6 @@
 #include "components/search_engines/search_engines_switches.h"
 #include "components/search_engines/template_url.h"
 #include "components/search_engines/template_url_service.h"
-#include "components/variations/entropy_provider.h"
 #include "components/variations/variations_associated_data.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -64,11 +63,6 @@ class KeywordProviderTest : public testing::Test {
   };
 
   KeywordProviderTest() : kw_provider_(nullptr) {
-    // Destroy the existing FieldTrialList before creating a new one to avoid
-    // a DCHECK.
-    field_trial_list_.reset();
-    field_trial_list_.reset(new base::FieldTrialList(
-        std::make_unique<variations::SHA1EntropyProvider>("foo")));
     variations::testing::ClearAllVariationParams();
   }
   ~KeywordProviderTest() override {}
@@ -90,7 +84,6 @@ class KeywordProviderTest : public testing::Test {
   static const TemplateURLService::Initializer kTestData[];
 
   base::test::TaskEnvironment task_environment_;
-  std::unique_ptr<base::FieldTrialList> field_trial_list_;
   scoped_refptr<KeywordProvider> kw_provider_;
   std::unique_ptr<MockAutocompleteProviderClient> client_;
 };

components/omnibox/browser/omnibox_field_trial_unittest.cc

@@ -17,7 +17,6 @@
 #include "build/build_config.h"
 #include "components/omnibox/common/omnibox_features.h"
 #include "components/search/search.h"
-#include "components/variations/entropy_provider.h"
 #include "components/variations/variations_associated_data.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/metrics_proto/omnibox_event.pb.h"
@@ -31,12 +30,18 @@ class OmniboxFieldTrialTest : public testing::Test {
   }
 
   void ResetFieldTrialList() {
-    // Destroy the existing FieldTrialList before creating a new one to avoid
-    // a DCHECK.
-    field_trial_list_.reset();
-    field_trial_list_.reset(new base::FieldTrialList(
-        std::make_unique<variations::SHA1EntropyProvider>("foo")));
+    scoped_feature_list_.Reset();
     variations::testing::ClearAllVariationParams();
+    scoped_feature_list_.Init();
+  }
+
+  void ResetAndEnableFeatureWithParameters(
+      const base::Feature& feature,
+      const base::FieldTrialParams& feature_parameters) {
+    scoped_feature_list_.Reset();
+    variations::testing::ClearAllVariationParams();
+    scoped_feature_list_.InitAndEnableFeatureWithParameters(feature,
+                                                            feature_parameters);
   }
 
   // Creates and activates a field trial.
@@ -73,7 +78,7 @@ class OmniboxFieldTrialTest : public testing::Test {
       int expected_delay_ms);
 
  private:
-  std::unique_ptr<base::FieldTrialList> field_trial_list_;
+  base::test::ScopedFeatureList scoped_feature_list_;
 
   DISALLOW_COPY_AND_ASSIGN(OmniboxFieldTrialTest);
 };
@@ -210,8 +215,7 @@ TEST_F(OmniboxFieldTrialTest, GetDemotionsByTypeWithFallback) {
 
 TEST_F(OmniboxFieldTrialTest, GetProviderMaxMatches) {
   {
-    base::test::ScopedFeatureList feature_list;
-    feature_list.InitAndEnableFeatureWithParameters(
+    ResetAndEnableFeatureWithParameters(
         omnibox::kUIExperimentMaxAutocompleteMatches,
         {{OmniboxFieldTrial::kUIMaxAutocompleteMatchesByProviderParam,
           "1:50,2:0"}});
@@ -223,8 +227,7 @@ TEST_F(OmniboxFieldTrialTest, GetProviderMaxMatches) {
                        AutocompleteProvider::Type::TYPE_HISTORY_QUICK));
   }
   {
-    base::test::ScopedFeatureList feature_list;
-    feature_list.InitAndEnableFeatureWithParameters(
+    ResetAndEnableFeatureWithParameters(
         omnibox::kUIExperimentMaxAutocompleteMatches,
         {{OmniboxFieldTrial::kUIMaxAutocompleteMatchesByProviderParam,
           "1:60,*:61,2:62"}});
@@ -236,6 +239,7 @@ TEST_F(OmniboxFieldTrialTest, GetProviderMaxMatches) {
                         AutocompleteProvider::Type::TYPE_HISTORY_QUICK));
   }
   {
+    ResetFieldTrialList();
     ASSERT_EQ(3ul, OmniboxFieldTrial::GetProviderMaxMatches(
                        AutocompleteProvider::Type::TYPE_BOOKMARK));
     ASSERT_EQ(3ul, OmniboxFieldTrial::GetProviderMaxMatches(