Order the parameters of a function at the definition site.

lib/compiler/implementation/js_backend/namer.dart

 // Copyright (c) 2011, 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.
 
 /**
  * Assigns JavaScript identifiers to Dart variables, class-names and members.
  */
 class Namer {
   final Compiler compiler;
 
@@ skipping 92 matching lines @@
     LibraryElement lib = element.getLibrary();
     if (element.kind == ElementKind.GENERATIVE_CONSTRUCTOR_BODY) {
       ConstructorBodyElement bodyElement = element;
       name = bodyElement.constructor.name;
     }
     FunctionSignature signature = element.computeSignature(compiler);
     String methodName =
         '${privateName(lib, name)}\$${signature.parameterCount}';
     if (!signature.optionalParametersAreNamed) {
       return methodName;
-    } else {
-      StringBuffer suffix = new StringBuffer();
-      signature.forEachOptionalParameter((Element element) {
-        String jsName = JsNames.getValid(element.name.slowToString());        
-        suffix.add('\$$jsName');
+    } else if (!signature.optionalParameters.isEmpty()) {
+      StringBuffer buffer = new StringBuffer();
+      signature.orderedOptionalParameters.forEach((Element element) {
+        buffer.add('\$${JsNames.getValid(element.name.slowToString())}');
       });
-      return '$methodName$suffix';
+      return '$methodName$buffer';
     }
   }
 
   String publicInstanceMethodNameByArity(SourceString name, int arity) {
     assert(!name.isPrivate());
     return '${name.slowToString()}\$$arity';
   }
 
   String instanceMethodInvocationName(LibraryElement lib, SourceString name,
                                       Selector selector) {
@@ skipping 173 matching lines @@
   }
 
   String safeName(String name) {
     if (jsReserved.contains(name) || name.startsWith('\$')) {
       name = "\$$name";
       assert(!jsReserved.contains(name));
     }
     return name;
   }
 }