Change IllegalArgumentException to ArgumentError.

pkg/intl/lib/intl.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * Internationalization object providing access to message formatting objects,
  * date formatting, parsing, bidirectional text relative to a specific locale.
  */
 #library('intl');
 
@@ skipping 103 matching lines @@
     // now. This should be moved, renamed, or generalized.
     if (newLocale == null) return systemLocale;
     if (_localeExists(newLocale)) {
       return newLocale;
     }
     for (var each in [canonicalizedLocale(newLocale), _shortLocale(newLocale)]) {
       if (_localeExists(each)) {
         return each;
       }
     }
-    throw new IllegalArgumentException("Invalid locale '$newLocale'");
+    throw new ArgumentError("Invalid locale '$newLocale'");
   }
 
   /** Return the short version of a locale name, e.g. 'en_US' => 'en' */
   static String _shortLocale(String aLocale) {
     if (aLocale.length < 2) return aLocale;
     return aLocale.substring(0, 2).toLowerCase();
   }
 
   /**
    * Return a locale name turned into xx_YY where it might possibly be
@@ skipping 76 matching lines @@
 /**
  * Initialize the message lookup mechanism. This is for internal use only.
  * User applications should import message_lookup_local.dart and call
  * initializeMessages
  */
 void initializeInternalMessageLookup(Function lookupFunction) {
   if (_messageLookup is UninitializedLocaleData) {
     _messageLookup = lookupFunction();
   }
 }