Use displayName in Error.stack rendering if present.

test/mjsunit/stack-traces-display-name.js

+// 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.
+
+var o = { f: function() { throw new Error(); } };
+o.g1 = function() { o.f() }
+o.g2 = o.g1;
+o.h = function() { o.g1() }
+o.f.displayName = "MySpecialFunction";
+
+try {
+  o.h();
+} catch (e) {
+  assertTrue(e.stack.indexOf("MySpecialFunction") != -1);
+}