Make int and double nullable by default

test/runtime/dart_runtime_test.dart

 // Copyright (c) 2015, 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.
 
 // Test code
 import 'dart:collection';
 import 'dart:mirrors';
 import 'package:unittest/unittest.dart';
+import 'package:dev_compiler/config.dart';
 import 'package:dev_compiler/runtime/dart_runtime.dart';
 
+final bool intIsNonNullable = TypeOptions.NONNULLABLE_TYPES.contains('int');
+final bool doubleIsNonNullable = TypeOptions.NONNULLABLE_TYPES.contains('double');
+
 class A {
   int x;
 }
 
 class B extends A {
   int y;
 }
 
 class C extends B {
   int z;
@@ skipping 63 matching lines @@
 
     checkType(5, int);
     checkType(5, dynamic);
     checkType(5, Object);
     checkType(5, num);
 
     checkType(5, bool, false);
     checkType(5, String, false);
 
     expect(cast(5, int), equals(5));
-    expect(() => cast(null, int), throws);
+    if (intIsNonNullable) {
+      expect(() => cast(null, int), throws);
+    } else {
+      expect(cast(null, int), equals(null));
+    }
   });
 
   test('dynamic', () {
     expect(isGroundType(dynamic), isTrue);
     checkType(new Object(), dynamic);
     checkType(null, dynamic);
 
     expect(cast(null, dynamic), equals(null));
   });
 
@@ skipping 153 matching lines @@
   test('arity', () {
     checkArity(bar1, 2, 2);
     checkArity(bar4, 2, 2);
     checkArity(bar6, 3, 3);
     checkArity(bar7, 2, 3);
     checkArity(bar8, 2, 2);
     checkArity(() {}, 0, 0);
     checkArity((a, [b]) {}, 1, 2);
   });
 }