Fix Array.{splice,slice} to set proper ElementsKind of result

test/mjsunit/elements-kind.js

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 287 matching lines @@
   assertKind(elements_kind.fast, e);
   assertFalse(%HaveSameMap(e, f));
   f[0] = 1.5;
   assertKind(elements_kind.fast_double, f);
   assertFalse(%HaveSameMap(e, f));
   f[0] = "bar";
   assertKind(elements_kind.fast, f);
   assertTrue(%HaveSameMap(e, f));
 }
 
+// Test that Array.splice() and Array.slice() return correct ElementsKinds.
+if (support_smi_only_arrays) {
+  var a = ["foo", "bar"];
+  assertKind(elements_kind.fast, a);
+  var b = a.splice(0, 1);
+  assertKind(elements_kind.fast, b);
+  var c = a.slice(0, 1);
+  assertKind(elements_kind.fast, c);
+}
+
 // Throw away type information in the ICs for next stress run.
 gc();