Mac Overlays: Add GPU back-pressure

ui/accelerated_widget_mac/display_link_mac.cc

Index: ui/accelerated_widget_mac/display_link_mac.cc
diff --git a/ui/accelerated_widget_mac/display_link_mac.cc b/ui/accelerated_widget_mac/display_link_mac.cc
index c9a30699a06fff31a5b8117c2cfb7f5d7b64e0c6..ec479d845b005dee9fd9a77c80a05abb07bf0660 100644
--- a/ui/accelerated_widget_mac/display_link_mac.cc
+++ b/ui/accelerated_widget_mac/display_link_mac.cc
@@ -27,6 +27,9 @@ namespace ui {
 // static
 scoped_refptr<DisplayLinkMac> DisplayLinkMac::GetForDisplay(
     CGDirectDisplayID display_id) {
+  if (!display_id)
+    return nullptr;
+
   // Return the existing display link for this display, if it exists.
   DisplayMap::iterator found = display_map_.Get().find(display_id);
   if (found != display_map_.Get().end()) {