Use ICU case conversion/transliterator for case conversion behind a flag

src/js/i18n.js

Index: src/js/i18n.js
diff --git a/src/js/i18n.js b/src/js/i18n.js
index 845289a91f10cf1416c4cff4b6698e27f412d6be..a2a0029b76c34cf48067dfe0c57f5f14c4489d74 100644
--- a/src/js/i18n.js
+++ b/src/js/i18n.js
@@ -144,6 +144,13 @@ var AVAILABLE_LOCALES = {
  */
 var DEFAULT_ICU_LOCALE = UNDEFINED;
 
+function GetDefaultICULocaleJS() {
+  if (IS_UNDEFINED(DEFAULT_ICU_LOCALE)) {
+    DEFAULT_ICU_LOCALE = %GetDefaultICULocale();
+  }
+  return DEFAULT_ICU_LOCALE;
+}
+
 /**
  * Unicode extension regular expression.
  */
@@ -448,11 +455,7 @@ function lookupMatcher(service, requestedLocales) {
   }
 
   // Didn't find a match, return default.
-  if (IS_UNDEFINED(DEFAULT_ICU_LOCALE)) {
-    DEFAULT_ICU_LOCALE = %GetDefaultICULocale();
-  }
-
-  return {'locale': DEFAULT_ICU_LOCALE, 'extension': '', 'position': -1};
+  return {'locale': GetDefaultICULocaleJS(), 'extension': '', 'position': -1};
 }
 
 
@@ -1992,6 +1995,23 @@ function cachedOrNewService(service, locales, options, defaults) {
   return new savedObjects[service](locales, useOptions);
 }
 
+function getCaseConversionLanguageId(locales) {
+  var locales = initializeLocaleList(locales);
+  var language = locales.length > 0 ? locales[0] : GetDefaultICULocaleJS();
+  var pos = %_Call(StringIndexOf, language, '-');
+  if (pos != -1)
+    language = %_Call(StringSubstring, language, 0, pos);
+  var CUSTOM_CASE_LANGUAGES = ['az', 'el', 'lt', 'tr'];
+  return %_Call(ArrayIndexOf, CUSTOM_CASE_LANGUAGES, language);
+}
+
+function localeConvertCase(s, locales, isToUpper) {
+  var caseConversionLanguageId = getCaseConversionLanguageId(locales);
+  if (caseConversionLanguageId == -1)
+    return isToUpper ? %StringToUpperCaseI18N(s) : %StringToLowerCaseI18N(s);
+  return %StringLocaleConvertCase(s, isToUpper, caseConversionLanguageId);
+}
+
 /**
  * Compares this and that, and returns less than 0, 0 or greater than 0 value.
  * Overrides the built-in method.
@@ -2044,6 +2064,45 @@ OverrideFunction(GlobalString.prototype, 'normalize', function() {
   }
 );
 
+OverrideFunction(GlobalString.prototype, 'toLowerCase', function() {
+    if (!IS_UNDEFINED(new.target)) {
+      throw MakeTypeError(kOrdinaryFunctionCalledAsConstructor);
+    }
+    CHECK_OBJECT_COERCIBLE(this, "String.prototype.toLowerCase");
+    var s = TO_STRING(this);
+    return %StringToLowerCaseI18N(s);
+  }
+);
+
+OverrideFunction(GlobalString.prototype, 'toUpperCase', function() {
+    if (!IS_UNDEFINED(new.target)) {
+      throw MakeTypeError(kOrdinaryFunctionCalledAsConstructor);
+    }
+    CHECK_OBJECT_COERCIBLE(this, "String.prototype.toLowerCase");
+    var s = TO_STRING(this);
+    return %StringToUpperCaseI18N(s);
+  }
+);
+
+OverrideFunction(GlobalString.prototype, 'toLocaleLowerCase', function() {
+    if (!IS_UNDEFINED(new.target)) {
+      throw MakeTypeError(kOrdinaryFunctionCalledAsConstructor);
+    }
+    CHECK_OBJECT_COERCIBLE(this, "String.prototype.toLocaleLowerCase");
+    return localeConvertCase(TO_STRING(this), arguments[0], false);
+  }
+);
+
+
+OverrideFunction(GlobalString.prototype, 'toLocaleUpperCase', function() {
+    if (!IS_UNDEFINED(new.target)) {
+      throw MakeTypeError(kOrdinaryFunctionCalledAsConstructor);
+    }
+    CHECK_OBJECT_COERCIBLE(this, "String.prototype.toLocaleUpperCase");
+    return localeConvertCase(TO_STRING(this), arguments[0], true);
+  }
+);
+
 
 /**
  * Formats a Number object (this) using locale and options values.