Spelling fixes e to i.

tests/language/named_parameters4_test.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.
 // Dart test program for testing named parameters.
 // Specifying named argument for not existing named parameter is run time error.
 
 import "package:expect/expect.dart";
 
-// This test is very similar to NamedParameters3Test, but exersizes a
+// This test is very similar to NamedParameters3Test, but exercises a
 // different corner case in the frog compiler. frog wasn't detecting unused
 // named arguments when no other arguments were expected. So, this test
 // purposely passes the exact number of positional parameters.
 
 int test(int a) {
   return a;
 }
 
 main() {
   bool foundError = false;
   try {
     test(10, x: 99); // 1 positional arg, as expected. Param x does not exist.
   } on NoSuchMethodError catch (e) {
     foundError = true;
   }
   Expect.equals(true, foundError);
 }