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:
/chrome/browser/permissions

This CL was uploaded by git cl split.

R=raymes@chromium.org

Bug: 1018667
Change-Id: If47bf45568a43449af37946d1362aad9189c6803
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1917525
Auto-Submit: Mikel Astiz <mastiz@chromium.org>
Reviewed-by: Raymes Khoury <raymes@chromium.org>
Commit-Queue: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715758}

chrome/browser/permissions/permission_context_base_unittest.cc

@@ -17,7 +17,6 @@
 #include "base/metrics/field_trial_params.h"
 #include "base/run_loop.h"
 #include "base/test/metrics/histogram_tester.h"
-#include "base/test/mock_entropy_provider.h"
 #include "base/test/scoped_feature_list.h"
 #include "build/build_config.h"
 #include "chrome/browser/content_settings/host_content_settings_map_factory.h"
@@ -155,21 +154,18 @@ class TestKillSwitchPermissionContext : public TestPermissionContext {
   TestKillSwitchPermissionContext(
       Profile* profile,
       const ContentSettingsType content_settings_type)
-      : TestPermissionContext(profile, content_settings_type),
-        field_trial_list_(std::make_unique<base::FieldTrialList>(
-            std::make_unique<base::MockEntropyProvider>())) {}
+      : TestPermissionContext(profile, content_settings_type) {
+    ResetFieldTrialList();
+  }
 
   void ResetFieldTrialList() {
-    // Destroy the existing FieldTrialList before creating a new one to avoid
-    // a DCHECK.
-    field_trial_list_.reset();
-    field_trial_list_ = std::make_unique<base::FieldTrialList>(
-        std::make_unique<base::MockEntropyProvider>());
+    scoped_feature_list_.Reset();
+    scoped_feature_list_.Init();
     variations::testing::ClearAllVariationParams();
   }
 
  private:
-  std::unique_ptr<base::FieldTrialList> field_trial_list_;
+  base::test::ScopedFeatureList scoped_feature_list_;
 
   DISALLOW_COPY_AND_ASSIGN(TestKillSwitchPermissionContext);
 };

chrome/browser/permissions/permission_manager_unittest.cc

@@ -8,7 +8,6 @@
 
 #include "base/bind.h"
 #include "base/macros.h"
-#include "base/test/mock_entropy_provider.h"
 #include "base/test/scoped_feature_list.h"
 #include "build/build_config.h"
 #include "chrome/browser/content_settings/host_content_settings_map_factory.h"
@@ -649,8 +648,6 @@ TEST_F(PermissionManagerTest, KillSwitchOnIsNotOverridable) {
           PermissionType::GEOLOCATION, kLocalHost));
 
   // Turn on kill switch for GEOLOCATION.
-  base::FieldTrialList field_trial_list(
-      std::make_unique<base::MockEntropyProvider>());
   variations::testing::ClearAllVariationParams();
   std::map<std::string, std::string> params;
   params[PermissionUtil::GetPermissionString(