Implements ES6 String.prototype.normalize method.

src/i18n.js

Index: src/i18n.js
diff --git a/src/i18n.js b/src/i18n.js
index a64c7e67844b01ebc134956e95c2cba87cd5a288..f23b222981ee7d743ac5c0def23e58acad4ce09e 100644
--- a/src/i18n.js
+++ b/src/i18n.js
@@ -45,6 +45,11 @@ var AVAILABLE_SERVICES = ['collator',
                           'dateformat',
                           'breakiterator'];
 
+var NORMALIZATION_FORMS = ['NFC',
+                           'NFD',
+                           'NFKC',
+                           'NFKD'];
+
 /**
  * Caches available locales for each service.
  */
@@ -1988,6 +1993,40 @@ $Object.defineProperty($String.prototype, 'localeCompare', {
 %FunctionRemovePrototype($String.prototype.localeCompare);
 %SetNativeFlag($String.prototype.localeCompare);
 
+/**
+ * Unicode normalization. This method is called with one argument that
+ * specifies the normalization form.
+ * If none is specified, "NFC" is assumed.
+ * If the form is not one of "NFC", "NFD", "NFKC", or "NFKD", then throw
+ * a RangeError Exception.
+ */
+$Object.defineProperty($String.prototype, 'normalize', {
+  value: function(that) {
+    if (%_IsConstructCall()) {
+      throw new $TypeError(ORDINARY_FUNCTION_CALLED_AS_CONSTRUCTOR);
+    }
+
+    if (IS_NULL_OR_UNDEFINED(this)) {
+      throw new $TypeError('Method invoked on undefined or null value.');
+    }
+
+    var form = $String(%_Arguments(0) || 'NFC');
+
+    var normalizationForm = NORMALIZATION_FORMS.indexOf(form);
+    if (normalizationForm !== -1) {
+      return %StringNormalize(this, normalizationForm);
+    }
+    throw new $RangeError('The normalization form should be one of '
+        + NORMALIZATION_FORMS.join(', ') + '.');
+  },
+  writable: true,
+  configurable: true,
+  enumerable: false
+});
+%FunctionSetName($String.prototype.normalize, 'normalize');
+%FunctionRemovePrototype($String.prototype.normalize);
+%SetNativeFlag($String.prototype.normalize);
+
 
 /**
  * Formats a Number object (this) using locale and options values.