Support new try/catch syntax.

lib/compiler/implementation/tree/unparser.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.
 
 // Returns null if no need to rename a node.
 typedef String Renamer(Node node);
 
 class Unparser implements Visitor {
   Renamer rename;
   StringBuffer sb;
@@ skipping 452 matching lines @@
   }
 
   visitCaseMatch(CaseMatch node) {
     add(node.caseKeyword.value);
     sb.add(" ");
     visit(node.expression);
     add(node.colonToken.value);
   }
 
   visitCatchBlock(CatchBlock node) {
+    addToken(node.onKeyword);
+    visit(node.type);
+    sb.add(' ');
     addToken(node.catchKeyword);
     visit(node.formals);
     sb.add(' ');
     visit(node.block);
   }
 
   visitTypedef(Typedef node) {
     addToken(node.typedefKeyword);
     if (node.returnType !== null) {
       visit(node.returnType);
       sb.add(' ');
     }
     visit(node.name);
     if (node.typeParameters !== null) {
       visit(node.typeParameters);
     }
     visit(node.formals);
     add(node.endToken.value);
   }
 }