Backport some tests in /components/sync_sessions 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
/components/sync_sessions.

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

This CL was uploaded by git cl split.

R=vitaliii@chromium.org

Bug: 891670
Change-Id: I7d613562534207fcb526a2e8cbd1bff08ddb28e6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1786847
Auto-Submit: Gabriel Charette <gab@chromium.org>
Reviewed-by: vitaliii <vitaliii@chromium.org>
Commit-Queue: vitaliii <vitaliii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#694221}

components/sync_sessions/favicon_cache_unittest.cc

@@ -302,7 +302,7 @@ class SyncFaviconCacheTest : public testing::Test {
   void RunUntilIdle() { task_environment_.RunUntilIdle(); }
 
  private:
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
   testing::NiceMock<favicon::MockFaviconService> mock_favicon_service_;
   FaviconCache cache_;
 
@@ -313,7 +313,8 @@ class SyncFaviconCacheTest : public testing::Test {
 };
 
 SyncFaviconCacheTest::SyncFaviconCacheTest()
-    : task_environment_(base::test::TaskEnvironment::MainThreadType::UI),
+    : task_environment_(
+          base::test::SingleThreadTaskEnvironment::MainThreadType::UI),
       cache_(&mock_favicon_service_, nullptr, kMaxSyncFavicons),
       sync_processor_(new TestChangeProcessor),
       sync_processor_wrapper_(new syncer::SyncChangeProcessorWrapperForTest(

components/sync_sessions/lost_navigations_recorder_unittest.cc

@@ -121,7 +121,7 @@ class LostNavigationsRecorderTest : public testing::Test {
   }
 
  private:
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
   int _id;
   LostNavigationsRecorder recorder_;
   syncer::TestDirectorySetterUpper dir_maker_;

components/sync_sessions/session_store_unittest.cc

@@ -175,7 +175,7 @@ class SessionStoreOpenTest : public ::testing::Test {
 
   ~SessionStoreOpenTest() override {}
 
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
   TestingPrefServiceSimple pref_service_;
   SessionSyncPrefs session_sync_prefs_;
   std::unique_ptr<MockSyncSessionsClient> mock_sync_sessions_client_;

components/sync_sessions/session_sync_bridge_unittest.cc

@@ -322,7 +322,7 @@ class SessionSyncBridgeTest : public ::testing::Test {
   syncer::ModelTypeStore* underlying_store() { return store_.get(); }
 
  private:
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
   const std::unique_ptr<syncer::ModelTypeStore> store_;
 
   // Dependencies.