Enable "system-ui" generic font family

third_party/WebKit/Source/platform/fonts/skia/FontCacheSkia.cpp

 /*
  * Copyright (c) 2006, 2007, 2008, 2009 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 193 matching lines @@
   if (creationParams.creationType() == CreateFontByFciIdAndTtcIndex) {
     if (Platform::current()->sandboxSupport())
       return typefaceForFontconfigInterfaceIdAndTtcIndex(
           creationParams.fontconfigInterfaceId(), creationParams.ttcIndex());
     return SkTypeface::MakeFromFile(creationParams.filename().data(),
                                     creationParams.ttcIndex());
   }
 #endif
 
   AtomicString family = creationParams.family();
+  DCHECK_NE(family, FontFamilyNames::system_ui);
   // If we're creating a fallback font (e.g. "-webkit-monospace"), convert the
   // name into the fallback name (like "monospace") that fontconfig understands.
   if (!family.length() || family.startsWith("-webkit-")) {
     name = getFallbackFontFamily(fontDescription).getString().utf8();
   } else {
     // convert the name to utf8
     name = family.utf8();
   }
 
 #if OS(WIN)
@@ skipping 38 matching lines @@
                                      fontDescription.isSyntheticBold(),
       ((fontDescription.style() == FontStyleItalic ||
         fontDescription.style() == FontStyleOblique) &&
        !tf->isItalic()) ||
           fontDescription.isSyntheticItalic(),
       fontDescription.orientation()));
 }
 #endif  // !OS(WIN)
 
 }  // namespace blink