Force SharedFunctionInfo::name() to be a flat string

This fact is depended upon by, at least, Parser::ParseLazy, and quite
likely by other code. There was already code in %FunctionSetName
enforcing this invariant. This patch adds similar code to
Factory::NewSharedFunctionInfo().

BUG=v8:4659
LOG=n

Review URL: https://codereview.chromium.org/1686193003

Cr-Commit-Position: refs/heads/master@{#33914}

src/factory.cc

@@ -2116,6 +2116,7 @@ Handle<SharedFunctionInfo> Factory::NewSharedFunctionInfo(
   Handle<SharedFunctionInfo> share = New<SharedFunctionInfo>(map, OLD_SPACE);
 
   // Set pointer fields.
+  name = String::Flatten(name, TENURED);
   share->set_name(*name);
   Handle<Code> code;
   if (!maybe_code.ToHandle(&code)) {

test/mjsunit/regress/regress-4659.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.
+//
+// Flags: --harmony-function-name
+
+var obj = {
+  get longerName(){
+    return 42;
+  }
+};
+assertEquals(42, obj.longerName);