fixes #177, FunctionDeclarationStatement and closing over `this`

lib/runtime/dart/_js_helper.js

 var _js_helper = dart.defineLibrary(_js_helper, {});
 var core = dart.import(core);
 var collection = dart.import(collection);
 var _internal = dart.import(_internal);
 var _foreign_helper = dart.import(_foreign_helper);
 var _js_embedded_names = dart.import(_js_embedded_names);
 var _interceptors = dart.lazyImport(_interceptors);
 var _js_names = dart.import(_js_names);
 var async = dart.import(async);
 var _isolate_helper = dart.lazyImport(_isolate_helper);
@@ skipping 2448 matching lines @@
       this[_message] = message;
       super.Error();
     }
     toString() {
       return this[_message].isEmpty ? 'Error' : `Error: ${this[_message]}`;
     }
   }
   // Function unwrapException: (dynamic) → dynamic
   function unwrapException(ex) {
     // Function saveStackTrace: (dynamic) → dynamic
-    function saveStackTrace(error) {
+    let saveStackTrace = error => {
       if (dart.is(error, core.Error)) {
         let thrownStackTrace = error.$thrownJsError;
         if (thrownStackTrace == null) {
           error.$thrownJsError = ex;
         }
       }
       return error;
-    }
+    };
     if (ex == null)
       return null;
     if (typeof ex !== "object")
       return ex;
     if ("dartException" in ex) {
       return saveStackTrace(ex.dartException);
     } else if (!("message" in ex)) {
       return ex;
     }
     let message = ex.message;
@@ skipping 1595 matching lines @@
   exports.jsonEncodeNative = jsonEncodeNative;
   exports.getIsolateAffinityTag = getIsolateAffinityTag;
   exports.LoadLibraryFunctionType = LoadLibraryFunctionType;
   exports.DeferredLoadCallback = DeferredLoadCallback;
   exports.loadDeferredLibrary = loadDeferredLibrary;
   exports.MainError = MainError;
   exports.missingMain = missingMain;
   exports.badMain = badMain;
   exports.mainHasTooManyParameters = mainHasTooManyParameters;
 })(_js_helper, core, collection, _internal, _foreign_helper, _js_embedded_names, _interceptors, _js_names, async, _isolate_helper);