Enable "system-ui" generic font family

third_party/WebKit/Source/platform/fonts/FontCache.h

 /*
  * Copyright (C) 2006, 2008 Apple Computer, Inc.  All rights reserved.
  * Copyright (C) 2007-2008 Torch Mobile, Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 97 matching lines @@
   ShapeCache* getShapeCache(const FallbackListCompositeKey&);
 
   void addClient(FontCacheClient*);
 
   unsigned short generation();
   void invalidate();
 
   SkFontMgr* fontManager() { return m_fontManager.get(); }
   static void setFontManager(const sk_sp<SkFontMgr>&);
 
+#if !OS(MACOSX)
+  static const AtomicString& systemFontFamily();
+#else
+  static const AtomicString& legacySystemFontFamily();
+#endif
+#if OS(LINUX)
+  static void setSystemFontFamily(const char*);
+#endif
+
 #if OS(WIN)
   static bool antialiasedTextEnabled() { return s_antialiasedTextEnabled; }
   static bool lcdTextEnabled() { return s_lcdTextEnabled; }
   static float deviceScaleFactor() { return s_deviceScaleFactor; }
   static void setAntialiasedTextEnabled(bool enabled) {
     s_antialiasedTextEnabled = enabled;
   }
   static void setLCDTextEnabled(bool enabled) { s_lcdTextEnabled = enabled; }
   static void setDeviceScaleFactor(float deviceScaleFactor) {
     s_deviceScaleFactor = deviceScaleFactor;
@@ skipping 130 matching lines @@
   WTF_MAKE_NONCOPYABLE(FontCachePurgePreventer);
 
  public:
   FontCachePurgePreventer() { FontCache::fontCache()->disablePurging(); }
   ~FontCachePurgePreventer() { FontCache::fontCache()->enablePurging(); }
 };
 
 }  // namespace blink
 
 #endif