Take Accept-Language into account in CJK font fallback for Android/Win

third_party/WebKit/Source/platform/fonts/android/FontCacheAndroid.cpp

 /*
  * Copyright (c) 2011 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 39 matching lines @@
     switch (localeToScriptCodeForFontSelection(locale)) {
     case USCRIPT_SIMPLIFIED_HAN:
         return "zh-Hans";
     case USCRIPT_TRADITIONAL_HAN:
         return "zh-Hant";
     default:
         return locale.ascii();
     }
 }
 
-void FontCache::acceptLanguagesChanged(const String&)
+static const char* toSkFontMgrLocaleForHan(UScriptCode script)
 {
-    // TODO(kojii): Take acceptLanguages into account for ambiguos scripts.
+    switch (script) {
+    case USCRIPT_KATAKANA_OR_HIRAGANA:
+        return "ja-jp";
+    case USCRIPT_HANGUL:
+        return "ko-kr";
+    case USCRIPT_SIMPLIFIED_HAN:
+        return "zh-Hans";
+    case USCRIPT_TRADITIONAL_HAN:
+        return "zh-Hant";
+    default:
+        ASSERT_NOT_REACHED();
+        return nullptr;
+    }
+}
+
+static const char* computeLocaleForHan(const String& acceptLanguages)
+{
+    // If defaultLanguage() can disambiguate the Unified Han, additional locales
+    // are not needed.
+    UScriptCode script = scriptCodeForHanFromLocale(defaultLanguage());
+    if (script != USCRIPT_COMMON)
+        return nullptr;
+
+    // Use acceptLanguages if it has a language that can disambiguate.
+    Vector<String> languages;
+    acceptLanguages.split(',', languages);
+    for (String token : languages) {
+        token = token.stripWhiteSpace();
+        script = scriptCodeForHanFromLocale(token);
+        if (script != USCRIPT_COMMON)
+            return toSkFontMgrLocaleForHan(script);
+    }
+
+    return nullptr;
+}
+
+static const char* localeForHan = nullptr;
+
+void FontCache::acceptLanguagesChanged(const String& acceptLanguages)

[drott, 2016/02/12 12:07:30]

Could we move this listener to a new singleton called sth like
AcceptLanguagesHanResolver, this would have roughly three methods: 

acceptLanguagesChanged(const String& acceptLanguages)
and then two methods for retrieval:
UScriptCode preferredHanScript()
char* preferredHanBcp47Locale()

The second method can internally call the first, and then practially do:
toSkFontMgrLocaleForHan.

Then the preferredHanBcp47Locale() could be used in
getFamilyNameForCharacterBelow directly, or in computeLocal for Han here.

+{
+    localeForHan = computeLocaleForHan(acceptLanguages);
 }
 
 static AtomicString getFamilyNameForCharacter(UChar32 c, const FontDescription& fontDescription)
 {
     RefPtr<SkFontMgr> fm = adoptRef(SkFontMgr::RefDefault());
-    const char* bcp47Locales[2];
+    const char* bcp47Locales[3];
     int localeCount = 0;
+    if (localeForHan)
+        bcp47Locales[localeCount++] = localeForHan;
     CString defaultLocale = toSkFontMgrLocale(defaultLanguage());
     bcp47Locales[localeCount++] = defaultLocale.data();
     CString fontLocale;
     if (!fontDescription.locale().isEmpty()) {
         fontLocale = toSkFontMgrLocale(fontDescription.locale());
         bcp47Locales[localeCount++] = fontLocale.data();
     }
     RefPtr<SkTypeface> typeface = adoptRef(fm->matchFamilyStyleCharacter(0, SkFontStyle(), bcp47Locales, localeCount, c));
     if (!typeface)
         return emptyAtom;
@@ skipping 28 matching lines @@
         break;
     default:
         // For other scripts, use the default generic family mapping logic.
         return familyName;
     }
 
     return getFamilyNameForCharacter(examplerChar, fontDescription);
 }
 
 } // namespace blink