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..683f3962bdf84a29e056d083f44da1f2e109f3ae 100644
--- a/third_party/WebKit/Source/platform/fonts/FontCache.cpp
+++ b/third_party/WebKit/Source/platform/fonts/FontCache.cpp
@@ -107,6 +107,29 @@ FontPlatformData* FontCache::getFontPlatformData(
     platformInit();
   }
 
+  if (creationParams.creationType() == CreateFontByFamily) {
+#if !OS(MACOSX)
+    if (creationParams.family() == FontFamilyNames::system_ui) {
+      const AtomicString& actualFamily = FontCache::systemFontFamily();
+#if OS(LINUX)
+      if (actualFamily.isEmpty() || actualFamily == FontFamilyNames::system_ui)
+        return nullptr;
+#else
+      DCHECK(!actualFamily.isEmpty() &&
+             actualFamily != FontFamilyNames::system_ui);
+#endif
+      return getFontPlatformData(fontDescription,
+                                 FontFaceCreationParams(actualFamily), true);
+    }
+#else

[drott, 2016/10/18 10:16:30]

Nit perhaps, but I am considering how we could make this more readable and
remove the #ifdef nesting here. Could you move this block up, first, and use
#ifdef OS(MACOSX), then just return getFontPlatformData, then #endif, then write
the rest? I think that would avoid the nesting.

[kojii, 2016/10/18 10:37:35]

Ok, it's still nesting IIUC but nest in #else might be better.

[kojii, 2016/10/18 10:42:40]

Note, this part will need some re-write, since when we add UMA, this function
doesn't have Document. I'm still seeking for the best place to convert
BlinkMacSystemFont in a following CL.

+    if (creationParams.family() == FontCache::legacySystemFontFamily()) {
+      return getFontPlatformData(
+          fontDescription, FontFaceCreationParams(FontFamilyNames::system_ui),
+          true);
+    }
+#endif
+  }
+
   float size = fontDescription.effectiveFontSize();
   unsigned roundedSize = size * FontCacheKey::precisionMultiplier();
   FontCacheKey key = fontDescription.cacheKey(creationParams);