[core] cleanup === and !==

lib/core/errors.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.
 
 class Error {
   const Error();
 }
 
 class AssertionError implements Error {
 }
@@ skipping 76 matching lines @@
       : this._existingArgumentNames = existingArgumentNames;
 
   String toString() {
     StringBuffer sb = new StringBuffer();
     for (int i = 0; i < _arguments.length; i++) {
       if (i > 0) {
         sb.add(", ");
       }
       sb.add(safeToString(_arguments[i]));
     }
-    if (_existingArgumentNames === null) {
+    if (_existingArgumentNames == null) {
       return "NoSuchMethodError : method not found: '$_functionName'\n"
           "Receiver: ${safeToString(_receiver)}\n"
           "Arguments: [$sb]";
     } else {
       String actualParameters = sb.toString();
       sb = new StringBuffer();
       for (int i = 0; i < _existingArgumentNames.length; i++) {
         if (i > 0) {
           sb.add(", ");
         }
@@ skipping 31 matching lines @@
 
 class OutOfMemoryError implements Error {
   const OutOfMemoryError();
   String toString() => "Out of Memory";
 }
 
 class StackOverflowError implements Error {
   const StackOverflowError();
   String toString() => "Stack Overflow";
 }