js_ast: Avoid precedence issue with negative numbers as receivers at calls

pkg/js_ast/lib/src/nodes.dart

Index: pkg/js_ast/lib/src/nodes.dart
diff --git a/pkg/js_ast/lib/src/nodes.dart b/pkg/js_ast/lib/src/nodes.dart
index 95c8819f1c88e971b501c6685c347c74398fdfba..b6d11aa9988096635af8327233c25e91f0540cf7 100644
--- a/pkg/js_ast/lib/src/nodes.dart
+++ b/pkg/js_ast/lib/src/nodes.dart
@@ -985,7 +985,7 @@ abstract class DeferredNumber extends DeferredToken implements Literal {
 
   int get value;
 
-  int get precedenceLevel => PRIMARY;
+  int get precedenceLevel => value.isNegative ? UNARY : PRIMARY;
 }
 
 /// Interace for a deferred string value. An implementation has to provide
@@ -1074,6 +1074,8 @@ class LiteralNumber extends Literal {
 
   LiteralNumber(this.value);
 
+  int get precedenceLevel => value.startsWith('-') ? UNARY : PRIMARY;
+  
   accept(NodeVisitor visitor) => visitor.visitLiteralNumber(this);
   LiteralNumber _clone() => new LiteralNumber(value);
 }