Make hashCode a getter and not a method.

tests/corelib/big_integer_vm_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.
 // Testing Bigints.
 // TODO(srdjan): Make sure the numbers are Bigint and not Mint or Smi.
 
 #library("BigIntegerTest.dart");
 
 class BigIntegerTest {
 
@@ skipping 150 matching lines @@
     testBigintMul();
     testBigintModulo();
     testBigintTruncDiv();
     testBigintDiv();
     testBigintNegate();
     testShiftAmount();
     Expect.equals(1234567890123456, (1234567890123456).abs());
     Expect.equals(1234567890123456, (-1234567890123456).abs());
     var a = 10000000000000000000;
     var b = 10000000000000000001;
-    Expect.equals(false, a.hashCode() == b.hashCode());
-    Expect.equals(true, a.hashCode() == (b - 1).hashCode());
+    Expect.equals(false, a.hashCode == b.hashCode);
+    Expect.equals(true, a.hashCode == (b - 1).hashCode);
   }
 }
 
 main() {
   BigIntegerTest.testMain();
 }