Enable "system-ui" generic font family

third_party/WebKit/Source/platform/fonts/linux/FontCacheLinux.cpp

 /*
  * Copyright (C) 2012 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:
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *     notice, this list of conditions and the following disclaimer in the
@@ skipping 25 matching lines @@
 
 FontCache::FontCache() : m_purgePreventCount(0) {
   if (s_staticFontManager) {
     adopted(s_staticFontManager);
     m_fontManager = sk_ref_sp(s_staticFontManager);
   } else {
     m_fontManager = nullptr;
   }
 }
 
+static AtomicString& mutableSystemFontFamily() {
+  DEFINE_STATIC_LOCAL(AtomicString, systemFontFamily, ());
+  return systemFontFamily;
+}
+
+// static
+const AtomicString& FontCache::systemFontFamily() {
+  return mutableSystemFontFamily();
+}
+
+// static
+void FontCache::setSystemFontFamily(const char* familyName) {
+  DCHECK(familyName && *familyName);
+  mutableSystemFontFamily() = familyName;
+}
+
 void FontCache::getFontForCharacter(
     UChar32 c,
     const char* preferredLocale,
     FontCache::PlatformFallbackFont* fallbackFont) {
   if (Platform::current()->sandboxSupport()) {
     WebFallbackFont webFallbackFont;
     Platform::current()->sandboxSupport()->getFallbackFontForCharacter(
         c, preferredLocale, &webFallbackFont);
     fallbackFont->name = String::fromUTF8(CString(webFallbackFont.name));
     fallbackFont->filename = webFallbackFont.filename;
@@ skipping 95 matching lines @@
   std::unique_ptr<FontPlatformData> platformData(
       new FontPlatformData(*substitutePlatformData));
   platformData->setSyntheticBold(shouldSetSyntheticBold);
   platformData->setSyntheticItalic(shouldSetSyntheticItalic);
   return fontDataFromFontPlatformData(platformData.get(), DoNotRetain);
 }
 
 #endif  // !OS(ANDROID)
 
 }  // namespace blink