Implement onMatchFamilyStyle for Mac.
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1612653002

Review URL: https://codereview.chromium.org/1612653002
diff --git a/src/ports/SkFontHost_mac.cpp b/src/ports/SkFontHost_mac.cpp
index 25030be..1d68c43 100644
--- a/src/ports/SkFontHost_mac.cpp
+++ b/src/ports/SkFontHost_mac.cpp
@@ -2339,8 +2339,9 @@
     }
 
     virtual SkTypeface* onMatchFamilyStyle(const char familyName[],
-                                           const SkFontStyle&) const override {
-        return nullptr;
+                                           const SkFontStyle& fontStyle) const override {
+        SkAutoTUnref<SkFontStyleSet> sset(this->matchFamily(familyName));
+        return sset->matchStyle(fontStyle);
     }
 
     virtual SkTypeface* onMatchFamilyStyleCharacter(const char familyName[], const SkFontStyle&,