Change IllegalArgumentException to ArgumentError.

lib/compiler/implementation/util/uri_extras.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.
 
 #library('uri_extras');
 
 #import('dart:math');
 #import('dart:uri');
 
 String relativize(Uri base, Uri uri, bool isWindows) {
   if (!base.path.startsWith('/')) {
     // Also throw an exception if [base] or base.path is null.
-    throw new IllegalArgumentException('Expected absolute path: ${base.path}');
+    throw new ArgumentError('Expected absolute path: ${base.path}');
   }
   if (!uri.path.startsWith('/')) {
     // Also throw an exception if [uri] or uri.path is null.
-    throw new IllegalArgumentException('Expected absolute path: ${uri.path}');
+    throw new ArgumentError('Expected absolute path: ${uri.path}');
   }
   bool equalsNCS(String a, String b) {
     return a.toLowerCase() == b.toLowerCase();
   }
 
   String normalize(String path) {
     if (isWindows) {
       return path.toLowerCase();
     } else {
       return path;
@@ skipping 28 matching lines @@
       sb.add('../');
     }
     for (int i = common; i < uriParts.length - 1; i++) {
       sb.add('${uriParts[i]}/');
     }
     sb.add('${uriParts.last()}');
     return sb.toString();
   }
   return uri.toString();
 }