Support positional optional parameters even if stubs are missing.

sdk/lib/_internal/compiler/js_lib/js_helper.dart

 // Copyright (c) 2013, 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 _js_helper;
 
 import 'dart:_js_embedded_names' show
     GET_TYPE_FROM_NAME,
     GET_ISOLATE_TAG,
     INTERCEPTED_NAMES,
@@ skipping 1059 matching lines @@
         arguments = new List.from(positionalArguments);
       }
       argumentCount = JS('int', '#.length', arguments);
     } else {
       arguments = [];
     }
 
     String selectorName = '${JS_GET_NAME("CALL_PREFIX")}\$$argumentCount';
     var jsFunction = JS('var', '#[#]', function, selectorName);
     if (jsFunction == null) {
+      var interceptor = getInterceptor(function);
+      jsFunction = JS('', '#["call*"]', interceptor);
 
-      // TODO(ahe): This might occur for optional arguments if there is no call
-      // selector with that many arguments.
-
-      return functionNoSuchMethod(function, positionalArguments, null);
+      if (jsFunction == null) {
+        return functionNoSuchMethod(function, positionalArguments, null);
+      }
+      ReflectionInfo info = new ReflectionInfo(jsFunction);
+      int maxArgumentCount = info.requiredParameterCount +
+          info.optionalParameterCount;
+      if (info.areOptionalParametersNamed || maxArgumentCount < argumentCount) {
+        return functionNoSuchMethod(function, positionalArguments, null);
+      }
+      arguments = new List.from(arguments);
+      for (int pos = argumentCount; pos < maxArgumentCount; pos++) {
+        arguments.add(info.defaultValue(pos));
+      }
     }
     // We bound 'this' to [function] because of how we compile
     // closures: escaped local variables are stored and accessed through
     // [function].
     return JS('var', '#.apply(#, #)', jsFunction, function, arguments);
   }
 
   static applyFunctionWithNamedArguments(Function function,
                                          List positionalArguments,
                                          Map<String, dynamic> namedArguments) {
@@ skipping 2625 matching lines @@
   // This is a function that will return a helper function that does the
   // iteration of the sync*.
   //
   // Each invocation should give a helper with fresh state.
   final dynamic /* js function */ _outerHelper;
 
   SyncStarIterable(this._outerHelper);
 
   Iterator get iterator => new SyncStarIterator(JS('', '#()', _outerHelper));
 }