Implement onMatchFamilyStyle for Mac.

src/ports/SkFontHost_mac.cpp

Index: src/ports/SkFontHost_mac.cpp
diff --git a/src/ports/SkFontHost_mac.cpp b/src/ports/SkFontHost_mac.cpp
index 25030be4132952eba43469649ef24c5e3827f716..1d68c433bf2243259cd1f7dfe804741f0b77763b 100644
--- a/src/ports/SkFontHost_mac.cpp
+++ b/src/ports/SkFontHost_mac.cpp
@@ -2339,8 +2339,9 @@ protected:
     }
 
     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&,