Support signed constants.

lib/compiler/implementation/tree/unparser.dart

Index: lib/compiler/implementation/tree/unparser.dart
diff --git a/lib/compiler/implementation/tree/unparser.dart b/lib/compiler/implementation/tree/unparser.dart
index b48e08599b820aa9f57f2e1579c4a9d22afbe30b..5ebb8a7147fd5bdfad85be648acd87dbf6cd7ef2 100644
--- a/lib/compiler/implementation/tree/unparser.dart
+++ b/lib/compiler/implementation/tree/unparser.dart
@@ -143,10 +143,14 @@ class Unparser implements Visitor {
 
   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) {