Support forEachClassMember on closure classes

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';
 
@@ skipping 115 matching lines @@
   default:
     x = 11;
     break;
   }
   x = toplevel;
   x = testIs(x);
   x = new Generic<int>().method(x);
   x = testAsGeneric(x);
   x = testAsFunction(x);
   print(x);
+  var f = (x) {
+    return 400 + x;
+  };
+  x = f(x);
   return x;
 }
 typedef NoArg();
 @NoInline()
 testIs(o) => o is Generic<int> || o is NoArg;
 @NoInline()
 testAsGeneric(o) => o as Generic<int>;
 @NoInline()
 testAsFunction(o) => o as NoArg;
 '''
@@ skipping 213 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;
 }