Rewrite how we handle synthesized constructors in the compiler. This was motivated by issue https:/…

sdk/lib/_internal/compiler/implementation/closure.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.
 
 library closureToClassMapper;
 
 import "elements/elements.dart";
 import "dart2jslib.dart";
 import "dart_types.dart";
 import "scanner/scannerlib.dart" show Token;
@@ skipping 24 matching lines @@
       ClosureClassMap cached = closureMappingCache[node];
       if (cached != null) return cached;
 
       ClosureTranslator translator =
           new ClosureTranslator(compiler, elements, closureMappingCache, namer);
 
       // The translator will store the computed closure-mappings inside the
       // cache. One for given node and one for each nested closure.
       if (node is FunctionExpression) {
         translator.translateFunction(element, node);
+      } else if (element.isSynthesized) {
+        return new ClosureClassMap(null, null, null, new ThisElement(element));
       } else {
         // Must be the lazy initializer of a static.
         assert(node is SendSet);
         translator.translateLazyInitializer(element, node);
       }
       assert(closureMappingCache[node] != null);
       return closureMappingCache[node];
     });
   }
 
@@ skipping 760 matching lines @@
   }
 
   visitTryStatement(TryStatement node) {
     // TODO(ngeoffray): implement finer grain state.
     bool oldInTryStatement = inTryStatement;
     inTryStatement = true;
     node.visitChildren(this);
     inTryStatement = oldInTryStatement;
   }
 }