Order the parameters of a function at the definition site.

lib/compiler/implementation/elements/elements.dart

Index: lib/compiler/implementation/elements/elements.dart
===================================================================
--- lib/compiler/implementation/elements/elements.dart	(revision 12903)
+++ lib/compiler/implementation/elements/elements.dart	(working copy)
@@ -945,6 +945,9 @@
   final int requiredParameterCount;
   final int optionalParameterCount;
   final bool optionalParametersAreNamed;
+
+  List<Element> _orderedOptionalParameters;
+
   FunctionSignature(this.requiredParameters,
                     this.optionalParameters,
                     this.requiredParameterCount,
@@ -968,11 +971,28 @@
     }
   }
 
+  List<Element> get orderedOptionalParameters {
+    if (_orderedOptionalParameters != null) return _orderedOptionalParameters;
+    List<Element> list = new List<Element>.from(optionalParameters);
+    if (optionalParametersAreNamed) {
+      list.sort((Element a, Element b) {
+        return a.name.slowToString().compareTo(b.name.slowToString());
+      });
+    }
+    _orderedOptionalParameters = list;
+    return list;
+  }
+
   void forEachParameter(void function(Element parameter)) {
     forEachRequiredParameter(function);
     forEachOptionalParameter(function);
   }
 
+  void orderedForEachParameter(void function(Element parameter)) {
+    forEachRequiredParameter(function);
+    orderedOptionalParameters.forEach(function);
+  }
+
   int get parameterCount => requiredParameterCount + optionalParameterCount;
 }