Bug 1690235. Fix creating variation CTFonts. r=lsalzman

This is an alternate approach to aadbc6deca05.

CTFontCreateWithGraphicsFont seems to give "LastResort" when used on a
system CGFont with variation applied on 10.12-10.14. We can avoid that
by using CTFontCreateWithGraphicsFont with a variation descriptor.

I'm only applying this approach to cairo for now to mimimize the risk
of this breaking something or causing the crashes that we were seeing
before.

See servo/core-foundation-rs#439 for
a standalone test case.

Differential Revision: https://phabricator.services.mozilla.com/D104581

Author: jrmuizel

gfx/2d/ScaledFontMac.cpp

@@ -18,7 +18,6 @@
 #ifdef MOZ_WIDGET_UIKIT
 #  include <CoreFoundation/CoreFoundation.h>
 #endif
-#include "gfxPlatform.h"  // just for HasVariationFontSupport()
 #include "nsCocoaFeatures.h"
 #include "mozilla/gfx/Logging.h"
 
@@ -375,17 +374,6 @@ bool UnscaledFontMac::GetFontDescriptor(FontDescriptorOutput aCb,
     return false;
   }
 
-  // Bug 1690235: using a font descriptor may fail for variation fonts
-  // on systems prior to 10.15, so we return false in this case.
-  if (gfxPlatform::GetPlatform()->HasVariationFontSupport() &&
-      !nsCocoaFeatures::OnCatalinaOrLater()) {
-    CFDataRef data = CGFontCopyTableForTag(mFont, 0x66766172);  // 'fvar'
-    if (data) {
-      CFRelease(data);
-      return false;
-    }
-  }
-
   AutoRelease<CFStringRef> psname(CGFontCopyPostScriptName(mFont));
   if (!psname) {
     return false;

gfx/cairo/cairo/src/cairo-quartz-font.c

@@ -364,7 +364,12 @@ CreateCTFontFromCGFontWithVariations(CGFontRef aCGFont, CGFloat aSize)
     // XXX Does this need to behave differently for installed fonts on High
     // Sierra, as in other similar places (bug 1455569)?
 
-    if (!Gecko_OnSierraExactly()) {
+    CFStringRef name = CGFontCopyPostScriptName(aCGFont);
+    // CTFontCreateWithGraphicsFont seems to give "LastResort"
+    // when used on a system CGFont with variation applied
+    bool system_font = CFStringHasPrefix(name, CFSTR("."));
+
+    if (!Gecko_OnSierraExactly() && !system_font) {
         return CTFontCreateWithGraphicsFont(aCGFont, aSize, NULL, NULL);
     }