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

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

Index: third_party/WebKit/Source/platform/fonts/FontCache.h
diff --git a/third_party/WebKit/Source/platform/fonts/FontCache.h b/third_party/WebKit/Source/platform/fonts/FontCache.h
index 3bd9064bbb6134115004c4fa1e1a3a3ec559df6e..c0df3f9f37de9bcd37c4eed991cc4fedd83a4de9 100644
--- a/third_party/WebKit/Source/platform/fonts/FontCache.h
+++ b/third_party/WebKit/Source/platform/fonts/FontCache.h
@@ -108,6 +108,7 @@ public:
     SkFontMgr* fontManager() { return m_fontManager.get(); }
     static void setFontManager(const sk_sp<SkFontMgr>&);
 
+    static const AtomicString& systemFontFamily();
 #if OS(WIN)
     static bool antialiasedTextEnabled() { return s_antialiasedTextEnabled; }
     static bool lcdTextEnabled() { return s_lcdTextEnabled; }
@@ -127,6 +128,8 @@ public:
     static int32_t statusFontHeight() { return s_statusFontHeight; }
     static const AtomicString& statusFontFamily() { return *s_statusFontFamilyName; }
     static void setUseSkiaFontFallback(bool useSkiaFontFallback) { s_useSkiaFontFallback = useSkiaFontFallback; }
+#elif OS(LINUX) || OS(ANDROID)
+    static void setSystemFontFamily(const char*);
 #endif
 
     typedef uint32_t FontFileKey;
@@ -205,6 +208,8 @@ private:
     static AtomicString* s_statusFontFamilyName;
     static int32_t s_statusFontHeight;
     static bool s_useSkiaFontFallback;
+#elif OS(LINUX)
+    static AtomicString* s_systemFontFamilyName;
 #endif
 
     friend class SimpleFontData; // For fontDataFromFontPlatformData