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

test/mjsunit/regress/regress-450895.js

Index: test/mjsunit/regress/regress-450895.js
diff --git a/test/mjsunit/regress/regress-449070.js b/test/mjsunit/regress/regress-450895.js
similarity index 77%
copy from test/mjsunit/regress/regress-449070.js
copy to test/mjsunit/regress/regress-450895.js
index 7a0f0a838cdd25817ab6a2d8f63c1ef9fbe6e526..48aa00d956c6f84fdcfe2e02cfc286c0f07180ba 100644
--- a/test/mjsunit/regress/regress-449070.js
+++ b/test/mjsunit/regress/regress-450895.js
@@ -1,10 +1,9 @@
 // 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
 
-try {
-  %NormalizeElements(this);
-} catch(e) {
-}
+var v = new Array();
+Object.freeze(v);
+v = v.concat(0.5);