Add support for execution of constructor body

pkg/kernel/testcases/interpreter/object_initializers_test.dart

 // Copyright (c) 2017, 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.
 
 library object_initializers_test;
 
 /// Simple program creating an object with field initializers.
 void main() {
   var a = new A('foo1', 'foo2');
   print(a.foo1);
@@ skipping 12 matching lines @@
   A(String foo1, String foo2)
       : foo1 = foo1,
         foo2 = foo2;
 }
 
 class B {
   String foo1 = fieldInitializer(1, 'foo1');
   String foo2 = fieldInitializer(1, 'foo2');
   String foo3 = fieldInitializer(1, 'foo3');
 
-  // TODO: uncomment when support for *this* in initializer list is added.
-  // B(this.foo1, this.foo2) : foo3 = foo2;
-  B(this.foo1, this.foo2) : foo3 = fieldInitializer(2, 'foo3');
+  B(this.foo1, this.foo2) : foo3 = foo2;
 }
 
 String fieldInitializer(int f, String s) {
   print('$s: $f');
   return '$s: $f';
 }