Backport some tests in /services/preferences to SingleThreadTaskEnvironment

These tests were previously migrated from single-threaded MessageLoop to
a multi-threaded TaskEnvironment (then named ScopedTaskEnvironment) as
part of crbug.com/891670.

//base OWNERS decided in retrospect that it was better to keep a
single-threaded option for TaskEnvironment and introduced
SingleThreadTaskEnvironment. This CL retrofits that decision for
/services/preferences.

This CL is a no-op if it passes CQ.

This CL was uploaded by git cl split.

R=jonross@chromium.org

Bug: 891670
Change-Id: I2267eede47df2efb13f39d8be4500a24f82d2de5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1787112
Auto-Submit: Gabriel Charette <gab@chromium.org>
Reviewed-by: Jonathan Ross <jonross@chromium.org>
Commit-Queue: Jonathan Ross <jonross@chromium.org>
Cr-Commit-Position: refs/heads/master@{#693758}

services/preferences/persistent_pref_store_impl_unittest.cc

@@ -73,7 +73,7 @@ class PersistentPrefStoreImplTest : public testing::Test {
   PersistentPrefStore* pref_store() { return pref_store_.get(); }
 
  private:
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
 
   std::unique_ptr<PersistentPrefStoreImpl> impl_;
 

services/preferences/pref_service_factory_unittest.cc

@@ -247,7 +247,7 @@ class PrefServiceFactoryTest : public testing::Test {
       quit_closure.Run();
   }
 
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
   service_manager::TestServiceManager test_service_manager_;
   base::ScopedTempDir profile_dir_;
   scoped_refptr<WriteablePrefStore> above_user_prefs_pref_store_;

services/preferences/pref_store_consistency_unittest.cc

@@ -202,7 +202,7 @@ class PersistentPrefStoreConsistencyTest : public testing::Test {
  private:
   scoped_refptr<PersistentPrefStore> pref_store_;
   std::unique_ptr<PersistentPrefStoreImpl> pref_store_impl_;
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
 };
 
 TEST_F(PersistentPrefStoreConsistencyTest, TwoPrefs) {

services/preferences/pref_store_impl_unittest.cc

@@ -102,7 +102,7 @@ class PrefStoreImplTest : public testing::Test {
   PrefStore* pref_store() { return pref_store_.get(); }
 
  private:
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
 
   std::unique_ptr<PrefStoreImpl> impl_;
 

services/preferences/public/cpp/tests/persistent_pref_store_client_unittest.cc

@@ -102,7 +102,7 @@ class PersistentPrefStoreClientTest : public testing::Test,
   void ClearMutableValues() override {}
   void OnStoreDeletionFromDisk() override {}
 
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
 
   std::unique_ptr<PrefService> pref_service_;
 

services/preferences/public/cpp/tests/pref_store_client_unittest.cc

@@ -66,7 +66,7 @@ class PrefStoreClientTest : public testing::Test {
   scoped_refptr<PrefStoreClient> store_;
 
   // Required by mojo binding code within PrefStoreClient.
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefStoreClientTest);
 };