[proxies] do not leak private symbols to proxy traps

test/mjsunit/harmony/proxies-has.js

Index: test/mjsunit/harmony/proxies-has.js
diff --git a/test/mjsunit/harmony/proxies-has.js b/test/mjsunit/harmony/proxies-has.js
index ffeb0312aad6884519c30d46a0a281463aa95af7..8eda812503ea642b54174ef60dcd7c3e1012de08 100644
--- a/test/mjsunit/harmony/proxies-has.js
+++ b/test/mjsunit/harmony/proxies-has.js
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --harmony-proxies
+// Flags: --harmony-proxies --harmony-reflect --allow-natives-syntax
 
 var target = {
   "target_one": 1
@@ -54,3 +54,15 @@ assertThrows("'nonconf' in proxy", TypeError);
 assertThrows("'target_one' in proxy", TypeError);
 assertFalse("target_two" in proxy);
 assertFalse("in_your_dreams" in proxy);
+
+(function testHasPrivateSymbol() {
+  var symbol = %CreatePrivateSymbol("secret");
+  var O = {};
+  var proxy = new Proxy(O, { has(t, name) { assertUnreachable(); }});
+  O[symbol] = "value";
+  proxy[symbol] = "value";
+  assertEquals(false, symbol in proxy);
+  assertEquals(false, Reflect.has(proxy, symbol));
+  assertEquals(true, symbol in O);
+  assertEquals(true, Reflect.has(O, symbol));
+})();