Fixed a couple of proxies-related unhandled exceptions.

test/mjsunit/regress/regress-crbug-506956.js

Index: test/mjsunit/regress/regress-crbug-506956.js
diff --git a/test/mjsunit/regress/regress-449070.js b/test/mjsunit/regress/regress-crbug-506956.js
similarity index 51%
copy from test/mjsunit/regress/regress-449070.js
copy to test/mjsunit/regress/regress-crbug-506956.js
index 7a0f0a838cdd25817ab6a2d8f63c1ef9fbe6e526..5862ddb296747f4622778a82db65ae2eda1e58c1 100644
--- a/test/mjsunit/regress/regress-449070.js
+++ b/test/mjsunit/regress/regress-crbug-506956.js
@@ -1,10 +1,12 @@
 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
-//
-// Flags: --allow-natives-syntax
+
+// Flags: --harmony-proxies
 
 try {
-  %NormalizeElements(this);
+  var p = Proxy.create({ getPropertyDescriptor: function() { throw "boom"; } });
+  var o = Object.create(p);
+  with (o) { delete unresolved_name; }
 } catch(e) {
 }