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

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

Index: third_party/WebKit/Source/platform/fonts/android/FontCacheAndroid.cpp
diff --git a/third_party/WebKit/Source/platform/fonts/android/FontCacheAndroid.cpp b/third_party/WebKit/Source/platform/fonts/android/FontCacheAndroid.cpp
index 335b243f3066233ece5ccbb28fe24987cb9ba115..293ab6d804eae7b010a754fe9cf37e0237def64c 100644
--- a/third_party/WebKit/Source/platform/fonts/android/FontCacheAndroid.cpp
+++ b/third_party/WebKit/Source/platform/fonts/android/FontCacheAndroid.cpp
@@ -57,16 +57,58 @@ static CString toSkFontMgrLocale(const String& locale)
     }
 }
 
-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;