Store named parameters in sorted lists instead of using maps.

lib/text/ast_to_text.dart

Index: lib/text/ast_to_text.dart
diff --git a/lib/text/ast_to_text.dart b/lib/text/ast_to_text.dart
index 55d6ebb8ada05996b594478b7f8b5909b5874585..9e9a093bb2b206a8b5415e8bc8ccc4974eafb88d 100644
--- a/lib/text/ast_to_text.dart
+++ b/lib/text/ast_to_text.dart
@@ -1391,10 +1391,7 @@ class Printer extends Visitor<Null> {
         writeComma();
       }
       writeSymbol('{');
-      writeList(node.namedParameters.keys, (name) {
-        writeType(node.namedParameters[name]);
-        writeWord(name);
-      });
+      writeList(node.namedParameters, visitNamedType);
       writeSymbol('}');
     }
     writeSymbol(')');
@@ -1402,6 +1399,13 @@ class Printer extends Visitor<Null> {
     writeType(node.returnType);
   }
 
+  visitNamedType(NamedType node) {
+    writeWord(node.name);
+    writeSymbol(':');
+    writeSpace();
+    writeType(node.type);
+  }
+
   visitTypeParameterType(TypeParameterType node) {
     writeTypeParameterReference(node.parameter);
   }