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

content/public/common/renderer_preferences.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
 // A struct for managing browser's settings that apply to the renderer or its
 // webview.  These differ from WebPreferences since they apply to Chromium's
 // glue layer rather than applying to just WebKit.
 //
 // Adding new values to this class probably involves updating
 // common/view_messages.h, browser/browser.cc, etc.
@@ skipping 121 matching lines @@
   // Determines whether plugins are allowed to enter fullscreen mode.
   bool plugin_fullscreen_allowed;
 
   // Whether video-overlay (hole-punching) should be used for the embedded
   // encrypted video.  Currently only used by Android.
   bool use_video_overlay_for_embedded_encrypted_video;
 
   // Country iso of the mobile network for content detection purpose.
   std::string network_contry_iso;
 
+#if defined(OS_LINUX)
+  std::string system_font_family_name;
+#endif
+
 #if defined(OS_WIN)
   // The default system font settings for caption, small caption, menu and
   // status messages. Used only by Windows.
   base::string16 caption_font_family_name;
   int32_t caption_font_height;
 
   base::string16 small_caption_font_family_name;
   int32_t small_caption_font_height;
 
   base::string16 menu_font_family_name;
@@ skipping 18 matching lines @@
   int32_t arrow_bitmap_width_horizontal_scroll_bar_in_dips;
 #endif
 
   // The default font size used for rendering on Linux.
   int default_font_size;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_COMMON_RENDERER_PREFERENCES_H_