Add ConstructorBodyEntity

tests/compiler/dart2js/kernel/compile_from_dill_test_helper.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.
 
 // Helper to test compilation equivalence between source and .dill based
 // compilation.
 library dart2js.kernel.compile_from_dill_test_helper;
 
 import 'dart:async';
 import 'dart:io';
@@ skipping 39 matching lines @@
     'main.dart': '''
 import 'dart:html';
 
 foo({named}) => 1;
 bar(a) => !a;
 class Class {
   var field;
   static var staticField;
 
   Class();
-  Class.named(this.field);
+  Class.named(this.field) {
+    staticField = 42;
+  } 
 
   method() {}
 }
  
 class SubClass extends Class {
   method() {
     super.method();
   }  
 }
 
@@ skipping 224 matching lines @@
       Map<String, BufferedOutputSink> map2 = collector2.outputMap[outputType];
       checkSets(map1.keys, map2.keys, 'output', equality);
       map1.forEach((String name, BufferedOutputSink output1) {
         BufferedOutputSink output2 = map2[name];
         Expect.stringEquals(output1.text, output2.text);
       });
     });
   }
   return ResultKind.success;
 }