Enable "system-ui" generic font family

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

Index: third_party/WebKit/Source/platform/fonts/FontCache.cpp
diff --git a/third_party/WebKit/Source/platform/fonts/FontCache.cpp b/third_party/WebKit/Source/platform/fonts/FontCache.cpp
index 500a8848955c2cc658349e3bc0c815cc5ccddbb4..0b2d2612b392d566e9c73785bd4272a2e37da751 100644
--- a/third_party/WebKit/Source/platform/fonts/FontCache.cpp
+++ b/third_party/WebKit/Source/platform/fonts/FontCache.cpp
@@ -98,9 +98,20 @@ FontCache* FontCache::fontCache() {
   return &globalFontCache;
 }
 
+static bool isSystemFontFamily(const FontFaceCreationParams& creationParams) {
+#if OS(MACOSX)
+  return creationParams.creationType() == CreateFontByFamily &&
+         (creationParams.family() == FontFamilyNames::system_ui ||
+          creationParams.family() == FontCache::legacySystemFontFamily());
+#else
+  return creationParams.creationType() == CreateFontByFamily &&
+         creationParams.family() == FontFamilyNames::system_ui;
+#endif
+}
+
 FontPlatformData* FontCache::getFontPlatformData(
     const FontDescription& fontDescription,
-    const FontFaceCreationParams& creationParams,
+    const FontFaceCreationParams& originalCreationParams,
     bool checkingAlternateName) {
   if (!gFontPlatformDataCache) {
     gFontPlatformDataCache = new FontPlatformDataCache;
@@ -108,6 +119,10 @@ FontPlatformData* FontCache::getFontPlatformData(
   }
 
   float size = fontDescription.effectiveFontSize();
+  const FontFaceCreationParams& creationParams =
+      isSystemFontFamily(originalCreationParams)
+          ? FontFaceCreationParams(systemFontFamily(size))
+          : originalCreationParams;
   unsigned roundedSize = size * FontCacheKey::precisionMultiplier();
   FontCacheKey key = fontDescription.cacheKey(creationParams);
 
@@ -271,6 +286,12 @@ PassRefPtr<SimpleFontData> FontCache::fontDataFromFontPlatformData(
 
 bool FontCache::isPlatformFontAvailable(const FontDescription& fontDescription,
                                         const AtomicString& family) {
+  if (family == FontFamilyNames::system_ui)
+    return true;
+#if OS(MACOSX)
+  if (family == FontCache::legacySystemFontFamily())
+    return true;
+#endif
   bool checkingAlternateName = true;
   return getFontPlatformData(
       fontDescription,