Remove old frog-style dummy bodies from dart2js native class tests

tests/compiler/dart2js_native/native_call_arity3_frog_test.dart

 // Copyright (c) 2012, 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.
 
 import "dart:_js_helper";
 import "package:expect/expect.dart";
 
 // Test similar to NativeCallArity1FrogTest, but with default values to
 // parameters set to null. These parameters should be treated as if they
 // do not have a default value for the native methods.
 
 @Native("A")
 class A {
   int foo(int x) native;
 }
 
 @Native("B")
 class B {
   int foo([x = null, y, z = null]) native;
 }
 
 // TODO(sra): Add a case where the parameters have default values.  Wait until
 // dart:html need non-null default values.
 
-A makeA() native { return new A(); }
-B makeB() native { return new B(); }
+A makeA() native;
+B makeB() native;
 
 void setup() native """
 function A() {}
 A.prototype.foo = function () { return arguments.length; };
 
 function B() {}
 B.prototype.foo = function () { return arguments.length; };
 
 makeA = function(){return new A;};
 makeB = function(){return new B;};
@@ skipping 39 matching lines @@
   Expect.equals(2, b.foo(null, 20));
   Expect.equals(3, b.foo(null, null, 30));
   Expect.throws(() => b.foo(10, 20, 30, 40));
 }
 
 main() {
   setup();
   testDynamicContext();
   testStaticContext();
 }