Remove MessageLoopForIO references

Remove references in /media/audio

MessageLoopForIO is going away soon. Use SingleThreadTaskExecutor for
main functions and SingleThreadTaskEnvironment for tests instead. Both
are no op changes.

This CL was uploaded by git cl split.

R=olka@chromium.org

Bug: 891670
Change-Id: Iea502221ede3aec4f88c76f3ac7ccb744a365b84
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1781151
Auto-Submit: Carlos Caballero <carlscab@google.com>
Commit-Queue: Olga Sharonova <olka@chromium.org>
Reviewed-by: Olga Sharonova <olka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#693702}

media/audio/audio_input_device_unittest.cc

@@ -8,7 +8,6 @@
 
 #include "base/memory/ptr_util.h"
 #include "base/memory/shared_memory.h"
-#include "base/message_loop/message_loop.h"
 #include "base/process/process_handle.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
@@ -67,7 +66,8 @@ class MockCaptureCallback : public AudioCapturerSource::CaptureCallback {
 
 // Regular construction.
 TEST(AudioInputDeviceTest, Noop) {
-  base::MessageLoopForIO io_loop;
+  base::test::SingleThreadTaskEnvironment task_environment(
+      base::test::SingleThreadTaskEnvironment::MainThreadType::IO);
   MockAudioInputIPC* input_ipc = new MockAudioInputIPC();
   scoped_refptr<AudioInputDevice> device(new AudioInputDevice(
       base::WrapUnique(input_ipc), AudioInputDevice::Purpose::kUserInput));

media/audio/audio_output_unittest.cc

@@ -7,9 +7,9 @@
 #include <memory>
 
 #include "base/memory/aligned_memory.h"
-#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/test/bind_test_util.h"
+#include "base/test/task_environment.h"
 #include "base/test/test_timeouts.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/time/time.h"
@@ -56,7 +56,8 @@ class AudioOutputTest : public ::testing::Test {
   }
 
  protected:
-  base::MessageLoopForIO message_loop_;
+  base::test::SingleThreadTaskEnvironment task_environment_{
+      base::test::SingleThreadTaskEnvironment::MainThreadType::IO};
   std::unique_ptr<AudioManager> audio_manager_;
   std::unique_ptr<AudioDeviceInfoAccessorForTests> audio_manager_device_info_;
   AudioParameters stream_params_;