Check for proper types from error handling code

test/mjsunit/regress/regress-596718.js

Index: test/mjsunit/regress/regress-596718.js
diff --git a/test/mjsunit/regress/regress-596718.js b/test/mjsunit/regress/regress-596718.js
new file mode 100644
index 0000000000000000000000000000000000000000..6116427e7329d5ae0f3c515565cdd385f2c587e3
--- /dev/null
+++ b/test/mjsunit/regress/regress-596718.js
@@ -0,0 +1,12 @@
+// Copyright 2016 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.
+
+Error.prepareStackTrace = function(e, frames) { return frames; }
+assertThrows(() => new Error().stack[0].getMethodName.call({}), TypeError);
+
+Error.prepareStackTrace = function(e, frames) { return frames.map(frame => new Proxy(frame, {})); }
+assertThrows(() => new Error().stack[0].getMethodName(), TypeError);
+
+Error.prepareStackTrace = function(e, frames) { return frames; }
+assertEquals(null, new Error().stack[0].getMethodName());