Make int and double nullable by default

test/checker/inferred_type_test.dart

Index: test/checker/inferred_type_test.dart
diff --git a/test/checker/inferred_type_test.dart b/test/checker/inferred_type_test.dart
index 0287b86e215209362671d7cc4f146f0fb2e4a606..553b2ada65ea1fcebbb09fcd192907eb9fc43888 100644
--- a/test/checker/inferred_type_test.dart
+++ b/test/checker/inferred_type_test.dart
@@ -42,7 +42,7 @@ main() {
         x = /*warning:DownCastLiteral*/null;
       }
     '''
-  });
+  }, nonnullableTypes: <String>['int', 'double']);
 
   // Error when inferred type is `int` and assigned null.
   testChecker({
@@ -52,7 +52,7 @@ main() {
         x = /*warning:DownCastLiteral*/null;
       }
     '''
-  });
+  }, nonnullableTypes: <String>['int', 'double']);
 
   // No error when declared type is `num` and assigned null.
   testChecker({