Set the font family for the "system-ui" generic font family on Linux

third_party/WebKit/Source/core/testing/Internals.idl

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2013 Apple 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.
@@ skipping 283 matching lines @@
 
     void setValueForUser(Element element, DOMString value);
 
     DOMString textSurroundingNode(Node node, long x, long y, unsigned long maxLength);
 
     void setFocused(boolean focused);
     void setInitialFocus(boolean reverse);
 
     boolean ignoreLayoutWithPendingStylesheets(Document document);
 
+    readonly attribute DOMString systemFontFamily;
+
     // These functions are for testing NetInfo. You must call clearNetworkConnectionInfoOverride() at the end.
     [RaisesException] void setNetworkConnectionInfoOverride(boolean onLine, DOMString type, double downlinkMaxMbps);
     void clearNetworkConnectionInfoOverride();
 
     // This function is for testing HitRegions on Canvas2D.
     unsigned long countHitRegions(CanvasRenderingContext2D context);
 
     boolean isInCanvasFontCache(Document document, DOMString fontString);
     unsigned long canvasFontCacheMaxFonts();
 
@@ skipping 40 matching lines @@
     DOMString getScrollAnimationState(Node node);
 
     DOMString getProgrammaticScrollAnimationState(Node node);
 
     ClientRect visualRect(Node node);
 
     OriginTrialsTest originTrialsTest();
 
     void crash();
 };