fix: use public APIs in place of private CTFontDescriptorIsSystemUIFont in ui/gfx (#26548)

patches/chromium/.patches

@@ -102,3 +102,4 @@ fix_properly_honor_printing_page_ranges.patch
 fix_use_electron_generated_resources.patch
 chore_expose_v8_initialization_isolate_callbacks.patch
 export_gin_v8platform_pageallocator_for_usage_outside_of_the_gin.patch
+use_public_apis_to_determine_if_a_font_is_a_system_font_in_mas_build.patch

patches/chromium/use_public_apis_to_determine_if_a_font_is_a_system_font_in_mas_build.patch

@@ -0,0 +1,37 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Samuel Attard <samuel.r.attard@gmail.com>
+Date: Tue, 17 Nov 2020 16:59:28 -0800
+Subject: use public APIs to determine if a font is a system font in MAS build
+
+CTFontDescriptorIsSystemUIFont is a private API, we're using an _interesting_ technique in the MAS build to determine if the font is a system font by checking if it's kCTFontPriorityAttribute is set to system priority.
+
+diff --git a/ui/gfx/platform_font_mac.mm b/ui/gfx/platform_font_mac.mm
+index fc6047806e3511f60b58a669fdf628e1a48eb05b..bcc29ac87cfc965eb4c3f06d959605d2cb259770 100644
+--- a/ui/gfx/platform_font_mac.mm
++++ b/ui/gfx/platform_font_mac.mm
+@@ -25,9 +25,11 @@
+ 
+ using Weight = Font::Weight;
+ 
++#if !defined(MAS_BUILD)
+ extern "C" {
+ bool CTFontDescriptorIsSystemUIFont(CTFontDescriptorRef);
+ }
++#endif
+ 
+ namespace {
+ 
+@@ -269,7 +271,13 @@ NSInteger ToNSFontManagerWeight(Weight weight) {
+   // TODO(avi, etienneb): Figure out this font stuff.
+   base::ScopedCFTypeRef<CTFontDescriptorRef> descriptor(
+       CTFontCopyFontDescriptor(font));
++#if defined(MAS_BUILD)
++  CFNumberRef priority = (CFNumberRef)CTFontDescriptorCopyAttribute(descriptor.get(), (CFStringRef)kCTFontPriorityAttribute);
++  SInt64 v;
++  if (CFNumberGetValue(priority, kCFNumberSInt64Type, &v) && v == kCTFontPrioritySystem) {
++#else
+   if (CTFontDescriptorIsSystemUIFont(descriptor.get())) {
++#endif
+     // Assume it's the standard system font. The fact that this much is known is
+     // enough.
+     return PlatformFontMac::SystemFontType::kGeneral;