Store named parameters in sorted lists instead of using maps.

lib/checks.dart

Index: lib/checks.dart
diff --git a/lib/checks.dart b/lib/checks.dart
index 8de3b9f70d1d1cd324ced9366be718f7815601f6..a450e2f3d68f0faafdc713af95077bd6db13650f 100644
--- a/lib/checks.dart
+++ b/lib/checks.dart
@@ -75,11 +75,26 @@ class CheckReferences extends RecursiveVisitor {
   }
 
   visitFunctionNode(FunctionNode node) {
+    for (int i = 1; i < node.namedParameters.length; ++i) {
+      if (node.namedParameters[i - 1].compareTo(node.namedParameters[i]) >= 0) {
+        throw 'Named parameters are not sorted on function found in $context';
+      }
+    }
     typeParameters.addAll(node.typeParameters);
     node.visitChildren(this);
     typeParameters.removeAll(node.typeParameters);
   }
 
+  visitFunctionType(FunctionType node) {
+    for (int i = 1; i < node.namedParameters.length; ++i) {
+      if (node.namedParameters[i - 1].compareTo(node.namedParameters[i]) >= 0) {
+        throw 'Named parameters are not sorted on function type found in '
+            '$context';
+      }
+    }
+    node.visitChildren(this);
+  }
+
   @override
   defaultMemberReference(Member node) {
     if (!members.contains(node)) {