Support signed constants.

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.
 
 class Unparser implements Visitor {
   final Renamer renamer;
   StringBuffer sb;
 
   Unparser([this.renamer = const Renamer()]);
 
@@ skipping 125 matching lines @@
       visit(node.elsePart);
     }
   }
 
   visitLiteralBool(LiteralBool node) {
     add(node.token.value);
   }
 
   visitLiteralDouble(LiteralDouble node) {
     add(node.token.value);
+    // -Lit is represented as a send.
+    if (node.token.kind == PLUS_TOKEN) add(node.token.next.value);
   }
 
   visitLiteralInt(LiteralInt node) {
     add(node.token.value);
+    // -Lit is represented as a send.
+    if (node.token.kind == PLUS_TOKEN) add(node.token.next.value);
   }
 
   visitLiteralString(LiteralString node) {
     add(node.token.value);
   }
 
   visitStringJuxtaposition(StringJuxtaposition node) {
     visit(node.first);
     sb.add(" ");
     visit(node.second);
@@ skipping 341 matching lines @@
       sb.add(' ');
     }
     visit(node.name);
     if (node.typeParameters !== null) {
       visit(node.typeParameters);
     }
     visit(node.formals);
     add(node.endToken.value);
   }
 }