Make hashCode a getter and not a method.

tests/corelib/null_test.dart

Index: tests/corelib/null_test.dart
diff --git a/tests/corelib/null_test.dart b/tests/corelib/null_test.dart
index 7879ac5532389a5f59aa6c66fb30e95ee3f01f5a..8f30e6cf47f560119625ab78f6667bcd0ca9aaa5 100644
--- a/tests/corelib/null_test.dart
+++ b/tests/corelib/null_test.dart
@@ -15,7 +15,7 @@ main() {
   // These shouldn't throw.
   x.runtimeType;
   x.toString();
-  x.hashCode();
+  x.hashCode;
 
   // operator== is inherited from Object. It's the same as identical.
   // It's not really testable.
@@ -23,8 +23,6 @@ main() {
   Expect.isTrue(x == null);
 
   // Methods can be closurized and yields the same result.
-  var hc = x.hashCode;
-  Expect.equals(null.hashCode(), hc());
   var ts = x.toString;
   Expect.equals(null.toString(), ts());