More strict non-equal cleanups in library code

corelib/src/expect.dart

 // Copyright (c) 2011, 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.
 
 class Expect {
 
   /**
    * Checks whether the expected and actual values are equal (using [:==:]).
    */
   static void equals(var expected, var actual, [String reason = null]) {
@@ skipping 214 matching lines @@
    *   Expect.throws(myThrowingFunction,
    *                 (e) { return e is MyException})
    * :]
    */
   static void throws(void f(),
                      [_CheckExceptionFn check = null,
                       String reason = null]) {
     try {
       f();
     } catch (var e) {
-      if (check != null) {
+      if (check !== null) {
         Expect.isTrue(check(e));
       }
       return;
     }
     String msg = _getMessage(reason);
     _fail('Expect.throws($msg) fails');
   }
 
   static String _getMessage(String reason)
       => (reason === null) ? "" : ", '$reason'";
 
   static void _fail(String message) {
     throw new ExpectException(message);
   }
 }
 
 typedef bool _CheckExceptionFn(exception);
 
 class ExpectException implements Exception {
   ExpectException(this.message);
   String toString() => message;
   String message;
 }