Make int and double nullable by default

test/runtime/dart_runtime_test.dart

Index: test/runtime/dart_runtime_test.dart
diff --git a/test/runtime/dart_runtime_test.dart b/test/runtime/dart_runtime_test.dart
index f890f2be6f71db51ee9056938f21b6863eb30217..9b2576248b437f39013c778af589c20e945221ab 100644
--- a/test/runtime/dart_runtime_test.dart
+++ b/test/runtime/dart_runtime_test.dart
@@ -6,8 +6,12 @@
 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;
 }
@@ -91,7 +95,11 @@ void main() {
     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', () {