Fix incorrect strict not-equal comparison when both arguments are constants.

tests/language/strict_equal_test.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.
 
 
 main() {
   for (int i = 0; i < 6000; i++) {
     Expect.isFalse(test1(5));
     Expect.isTrue(test1(3));
 
     Expect.isTrue(test2(5));
     Expect.isFalse(test2(3));
 
     Expect.isTrue(test2r(5));
     Expect.isFalse(test2r(3));
 
     Expect.isTrue(test3());
 
     Expect.equals(2, test4(5));
     Expect.equals(1, test4(3));
 
     Expect.equals(1, test5(5));
     Expect.equals(2, test5(3));
 
     Expect.equals(1, test6());
+
+    Expect.isFalse(test7());
+    Expect.equals(2, test8());
   }
 }
 
 
 test1(a) {
   return a === 3;
 }
 
 test2(a) {
   return a !== 3;
@@ skipping 32 matching lines @@
   if (get5() === 5) {
     return 1;
   } else {
     return 2;
   }
 }
 
 get5() {
   return 5;
 }
+
+test7() {
+  return null !== null;
+}
+
+
+test8() {
+  if (null !== null) {
+    return 1;
+  } else {
+    return 2;
+  }
+}