Set the main thread of the audio process as type UI on Mac

This ensures that the main thread as a CFRunLoop, which is required
by audio APIs on Mac.

Bug: 841845
Change-Id: I10be74d77c1585014a63896099eb2b4acb5b345b
Reviewed-on: https://chromium-review.googlesource.com/1054227
Commit-Queue: Guido Urdaneta <guidou@chromium.org>
Commit-Queue: Olga Sharonova <olka@chromium.org>
Reviewed-by: Olga Sharonova <olka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#557597}

chrome/browser/chrome_content_browser_client.cc

@@ -276,6 +276,7 @@
 #include "sandbox/win/src/sandbox_policy.h"
 #elif defined(OS_MACOSX)
 #include "chrome/browser/chrome_browser_main_mac.h"
+#include "services/audio/public/mojom/constants.mojom.h"
 #include "services/video_capture/public/mojom/constants.mojom.h"
 #elif defined(OS_CHROMEOS)
 #include "ash/public/interfaces/constants.mojom.h"
@@ -2099,9 +2100,11 @@ void ChromeContentBrowserClient::AdjustUtilityServiceProcessCommandLine(
 #endif  // BUILDFLAG(ENABLE_MUS)
 
 #if defined(OS_MACOSX)
-  // On Mac, the video-capture service requires a CFRunLoop, provided by a UI
-  // message loop, to run AVFoundation code. See https://crbug.com/834581
-  if (identity.name() == video_capture::mojom::kServiceName)
+  // On Mac, the video-capture and audio services require a CFRunLoop, provided
+  // by a UI message loop, to run AVFoundation and CoreAudio code.
+  // See https://crbug.com/834581
+  if (identity.name() == video_capture::mojom::kServiceName ||
+      identity.name() == audio::mojom::kServiceName)
     command_line->AppendSwitch(switches::kMessageLoopTypeUi);
 #endif
 }