emit interfaces before use

lib/src/js/printer.dart

 // Copyright (c) 2012, 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.
 
 part of js_ast;
 
 
 class JavaScriptPrintingOptions {
   final bool shouldCompressOutput;
   final bool minifyLocalVariables;
@@ skipping 944 matching lines @@
   }
 
   visitClassExpression(ClassExpression node) {
     out('class ');
     visit(node.name);
     if (node.heritage != null) {
       out(' extends ');
       visit(node.heritage);
     }
     spaceOut();
-    out('{');
-    lineOut();
-    indentMore();
-    for (var method in node.methods) {
+    if (node.methods.isNotEmpty) {
+      out('{');
+      lineOut();
+      indentMore();
+      for (var method in node.methods) {
+        indent();
+        visit(method);
+        lineOut();
+      }
+      indentLess();
       indent();
-      visit(method);
-      lineOut();
+      out('}');
+    } else {
+      out('{}');
     }
-    indentLess();
-    indent();
-    out('}');
   }
 
   visitMethod(Method node) {
     if (node.isStatic) {
       out('static ');
     }
     if (node.isGetter) {
       out('get ');
     } else if (node.isSetter) {
       out('set ');
@@ skipping 379 matching lines @@
         codes.add(nthLetter((n ~/ nameSpaceSize) % LETTERS));
       }
       codes.add(charCodes.$0 + digit);
       newName = new String.fromCharCodes(codes);
     }
     assert(new RegExp(r'[a-zA-Z][a-zA-Z0-9]*').hasMatch(newName));
     maps.last[oldName] = newName;
     return newName;
   }
 }