fix #577 - correctly toString ES Symbols

test/browser/runtime_tests.js

Index: test/browser/runtime_tests.js
diff --git a/test/browser/runtime_tests.js b/test/browser/runtime_tests.js
index c3d39a3bc143f8a2ac413a51526af053f36a16ac..f30872f326ecac57ba82c149092e873bd0bcc553 100644
--- a/test/browser/runtime_tests.js
+++ b/test/browser/runtime_tests.js
@@ -1163,4 +1163,9 @@ suite('primitives', function() {
     list[0] = 42;
     assert.throws(() => list.add(42));
   });
+
+  test('toString on ES Symbol', () => {
+    let sym = Symbol('_foobar');
+    assert.equal(dart.toString(sym), 'Symbol(_foobar)');
+  });
 });