Switch media_stream_audio_processor.cc to use Blink's cross thread mechanisms

This is a follow up of [1].

[1] https://crrev.com/c/1710237

BUG=704136,923394
R=guidou@chromium.org

Change-Id: I34829b50b263f47cd8d4b6fc9b41df60b57ede0b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1715164
Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Cr-Commit-Position: refs/heads/master@{#681274}

third_party/blink/renderer/platform/exported/mediastream/media_stream_audio_processor.cc

@@ -12,7 +12,6 @@
 #include <utility>
 #include <vector>
 
-#include "base/bind.h"
 #include "base/feature_list.h"
 #include "base/metrics/field_trial.h"
 #include "base/metrics/field_trial_params.h"
@@ -32,6 +31,8 @@
 #include "third_party/blink/public/platform/platform.h"
 #include "third_party/blink/public/web/modules/webrtc/webrtc_audio_device_impl.h"
 #include "third_party/blink/renderer/platform/mediastream/aec_dump_agent_impl.h"
+#include "third_party/blink/renderer/platform/scheduler/public/post_cross_thread_task.h"
+#include "third_party/blink/renderer/platform/wtf/cross_thread_functional.h"
 #include "third_party/webrtc/api/audio/echo_canceller3_config.h"
 #include "third_party/webrtc/api/audio/echo_canceller3_config_json.h"
 #include "third_party/webrtc/api/audio/echo_canceller3_factory.h"
@@ -39,6 +40,17 @@
 #include "third_party/webrtc/modules/audio_processing/typing_detection.h"
 #include "third_party/webrtc_overrides/task_queue_factory.h"
 
+namespace WTF {
+
+template <typename T>
+struct CrossThreadCopier<rtc::scoped_refptr<T>> {
+  STATIC_ONLY(CrossThreadCopier);
+  using Type = rtc::scoped_refptr<T>;
+  static Type Copy(Type pointer) { return pointer; }
+};
+
+}  // namespace WTF
+
 namespace blink {
 
 using EchoCancellationType =
@@ -727,10 +739,10 @@ int MediaStreamAudioProcessor::ProcessData(const float* const* process_ptrs,
     base::subtle::Release_Store(&typing_detected_, typing_detected);
   }
 
-  main_thread_runner_->PostTask(
-      FROM_HERE,
-      base::BindOnce(&MediaStreamAudioProcessor::UpdateAecStats,
-                     rtc::scoped_refptr<MediaStreamAudioProcessor>(this)));
+  PostCrossThreadTask(
+      *main_thread_runner_, FROM_HERE,
+      CrossThreadBindOnce(&MediaStreamAudioProcessor::UpdateAecStats,
+                          rtc::scoped_refptr<MediaStreamAudioProcessor>(this)));
 
   // Return 0 if the volume hasn't been changed, and otherwise the new volume.
   const int recommended_volume = ap->recommended_stream_analog_level();