Further cleanup of OS_MACOSX in media

Bug: 1105907
Change-Id: I762e0a18817149a506948e9a0392fdac1b7cfa9d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2328339
Auto-Submit: Avi Drissman <avi@chromium.org>
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#793260}

media/audio/audio_manager.h

@@ -44,7 +44,7 @@ class MEDIA_EXPORT AudioManager {
   // AudioLogFactory; as such |audio_log_factory| must outlive the AudioManager.
   //
   // The manager will use |audio_thread->GetTaskRunner()| for audio IO.
-  // On OS_MACOSX, CoreAudio requires that |audio_thread->GetTaskRunner()|
+  // On OS_MAC, CoreAudio requires that |audio_thread->GetTaskRunner()|
   // must belong to the main thread of the process, which in our case is sadly
   // the browser UI thread. Failure to execute calls on the right thread leads
   // to crashes and odd behavior. See http://crbug.com/158170.