Backport some tests in...

Backport some tests in /media/mojo/services/mojo_audio_output_stream_provider_unittest.cc 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
/media/mojo/services/mojo_audio_output_stream_provider_unittest.cc.

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

This CL was uploaded by git cl split.

R=olka@chromium.org

Bug: 891670
Change-Id: I6db90bfd72373e3fef77b101d7c940b4b7de9ffb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1786854
Auto-Submit: Gabriel Charette <gab@chromium.org>
Reviewed-by: Olga Sharonova <olka@chromium.org>
Commit-Queue: Olga Sharonova <olka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#693707}

media/mojo/services/mojo_audio_output_stream_provider_unittest.cc

@@ -68,7 +68,7 @@ std::unique_ptr<AudioOutputDelegate> CreateFakeDelegate(
 }  // namespace
 
 TEST(MojoAudioOutputStreamProviderTest, AcquireTwice_BadMessage) {
-  base::test::TaskEnvironment task_environment;
+  base::test::SingleThreadTaskEnvironment task_environment;
   bool got_bad_message = false;
   mojo::core::SetDefaultProcessErrorCallback(
       base::BindRepeating([](bool* got_bad_message,
@@ -104,7 +104,7 @@ TEST(MojoAudioOutputStreamProviderTest, AcquireTwice_BadMessage) {
 
 TEST(MojoAudioOutputStreamProviderTest,
      Bitstream_BadMessageOnNonAndoirdPlatforms) {
-  base::test::TaskEnvironment task_environment;
+  base::test::SingleThreadTaskEnvironment task_environment;
   bool got_bad_message = false;
   mojo::core::SetDefaultProcessErrorCallback(
       base::BindRepeating([](bool* got_bad_message,