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

tests/compiler/dart2js_native/js_constant_test.dart

Index: tests/compiler/dart2js_native/js_constant_test.dart
diff --git a/tests/compiler/dart2js_native/js_constant_test.dart b/tests/compiler/dart2js_native/js_constant_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..19b2e6f9f1fe6f3055310886213bb895ea5376a3
--- /dev/null
+++ b/tests/compiler/dart2js_native/js_constant_test.dart
@@ -0,0 +1,44 @@
+// Copyright (c) 2015, 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.
+
+import 'dart:_foreign_helper' show JS;
+import "package:expect/expect.dart";
+
+// Negative constant numbers must be generated as negation, not just a literal
+// with a sign, i.e.
+//
+//     (-5).toString()
+//
+// not
+//
+//     -5 .toString()
+//
+// The unparethesized version is `-(5 .toString())`, which creates the string
+// `"5"`, then converts it to a number for negation, giving a number result
+// instead of a string result.
+
+@NoInline()
+checkString(r) {
+  Expect.isTrue(r is String,
+      'Expected string, found ${r} of type ${r.runtimeType}');
+}
+
+test1() {
+  checkString(JS('', '#.toString()', -5));
+}
+
+test2() {
+  checkString(JS('', '#.toString()', -1.5));
+}
+
+test3() {
+  checkString(JS('', '#.toString()', -0.0));
+}
+
+
+main() {
+  test1();
+  test2();
+  test3();
+}