Support concatenating with zero-size arrays with DICTIONARY_ELEMENTS in Runtime_ArrayConcat.

BUG=chromium:450895
LOG=y

Review URL: https://codereview.chromium.org/849693003

Cr-Commit-Position: refs/heads/master@{#26219}

src/runtime/runtime-array.cc

@@ -850,6 +850,7 @@ RUNTIME_FUNCTION(Runtime_ArrayConcat) {
             }
             case FAST_HOLEY_ELEMENTS:
             case FAST_ELEMENTS:
+            case DICTIONARY_ELEMENTS:
               DCHECK_EQ(0, length);
               break;
             default:

test/mjsunit/regress/regress-450895.js

+// 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
+
+var v = new Array();
+Object.freeze(v);
+v = v.concat(0.5);