Bug 1703522. Allow IOSurface capture by default. r=pehrsons

This cuts the time spent in CaptureFrame for a buffer size of 3072x1920
from ~80ms to ~22ms for me.  It makes it so that we use the IOSurfaces
provided to the CGDisplayStreamCreate handler instead of calling
CGDisplayCreateImage.

It was enable by default in Chromium in 2018 via
https://source.chromium.org/chromium/chromium/src/+/09cd5826e743af9dbcbde8ab36f73f5e0bd55f6c

Differential Revision: https://phabricator.services.mozilla.com/D157273

Author: jrmuizel

dom/media/systemservices/video_engine/desktop_capture_impl.cc

@@ -28,6 +28,7 @@
 #include "modules/desktop_capture/desktop_frame.h"
 #include "modules/desktop_capture/desktop_capture_options.h"
 #include "modules/video_capture/video_capture.h"
+#include "mozilla/StaticPrefs_media.h"
 
 #if defined(_WIN32)
 #  include "platform_uithread.h"
@@ -335,6 +336,12 @@ int32_t DesktopCaptureImpl::LazyInitDesktopCapturer() {
   // Leave desktop effects enabled during WebRTC captures.
   options.set_disable_effects(false);
 
+#if defined(WEBRTC_MAC)
+  if (mozilla::StaticPrefs::media_webrtc_capture_allow_iosurface()) {
+    options.set_allow_iosurface(true);
+  }
+#endif
+
   if (_deviceType == CaptureDeviceType::Screen) {
     std::unique_ptr<DesktopCapturer> pScreenCapturer =
         DesktopCapturer::CreateScreenCapturer(options);

modules/libpref/init/StaticPrefList.yaml

@@ -10081,6 +10081,11 @@
   value: @IS_EARLY_BETA_OR_EARLIER@
   mirror: always
 
+- name: media.webrtc.capture.allow-iosurface
+  type: RelaxedAtomicBool
+  value: true
+  mirror: always
+
 - name: media.block-autoplay-until-in-foreground
   type: bool
 #if !defined(MOZ_WIDGET_ANDROID)