Backport some tests in /components/drive 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/drive.

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

This CL was uploaded by git cl split.

R=kinaba@chromium.org

Bug: 891670
Change-Id: I0899e178d3699ec8eb8f78f5dcefc3b4bf452a3d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1787115
Auto-Submit: Gabriel Charette <gab@chromium.org>
Reviewed-by: Kazuhiro Inaba <kinaba@chromium.org>
Commit-Queue: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#694570}

components/drive/drive_uploader_unittest.cc

@@ -420,7 +420,7 @@ class DriveUploaderTest : public testing::Test {
   void SetUp() override { ASSERT_TRUE(temp_dir_.CreateUniqueTempDir()); }
 
  protected:
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
   base::ScopedTempDir temp_dir_;
 };
 

components/drive/local_file_reader_unittest.cc

@@ -56,7 +56,7 @@ class LocalFileReaderTest : public ::testing::Test {
         std::make_unique<LocalFileReader>(worker_thread_->task_runner().get());
   }
 
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
   base::ScopedTempDir temp_dir_;
   std::unique_ptr<base::Thread> worker_thread_;
   std::unique_ptr<LocalFileReader> file_reader_;

components/drive/service/fake_drive_service_unittest.cc

@@ -227,7 +227,7 @@ class FakeDriveServiceTest : public testing::Test {
     return about_resource->largest_change_id();
   }
 
-  base::test::TaskEnvironment task_environment_;
+  base::test::SingleThreadTaskEnvironment task_environment_;
   FakeDriveService fake_service_;
 };