Reenable realtime audio threads on 2-core Chrome OS.

Workaround shouldn't be needed anymore after crrev.com/530835.
Reenabling realtime priority should reduce audio glitches.

This really shouldn't cause any regressions, but adding the old
bugs as FYI just in case.

Bug: 754213,734490,710245,770312,803419
Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I2f7c6c793fade47a205a896a25468a7312ba55de
Reviewed-on: https://chromium-review.googlesource.com/913272Reviewed-by: Olga Sharonova <olka@chromium.org>
Commit-Queue: Max Morin <maxmorin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#536069}

media/audio/audio_device_thread.cc

@@ -9,22 +9,6 @@
 #include "base/logging.h"
 #include "base/sys_info.h"
 
-namespace {
-
-base::ThreadPriority GetAudioThreadPriority() {
-#if defined(OS_CHROMEOS)
-  // On Chrome OS, there are priority inversion issues with having realtime
-  // threads on systems with only two cores, see crbug.com/710245.
-  return base::SysInfo::NumberOfProcessors() > 2
-             ? base::ThreadPriority::REALTIME_AUDIO
-             : base::ThreadPriority::NORMAL;
-#else
-  return base::ThreadPriority::REALTIME_AUDIO;
-#endif
-}
-
-}  // namespace
-
 namespace media {
 
 // AudioDeviceThread::Callback implementation
@@ -66,8 +50,9 @@ AudioDeviceThread::AudioDeviceThread(Callback* callback,
                                      base::SyncSocket::Handle socket,
                                      const char* thread_name)
     : callback_(callback), thread_name_(thread_name), socket_(socket) {
-  CHECK(base::PlatformThread::CreateWithPriority(0, this, &thread_handle_,
-                                                 GetAudioThreadPriority()));
+  CHECK(base::PlatformThread::CreateWithPriority(
+      0, this, &thread_handle_, base::ThreadPriority::REALTIME_AUDIO));
+
   DCHECK(!thread_handle_.is_null());
 }