Faster moving FixedArray elements around.

test/mjsunit/array-unshift.js

 // Copyright 2010 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 112 matching lines @@
       throw 'Should have thrown RangeError';
     } catch (e) {
       assertTrue(e instanceof RangeError);
     }
 
     // Check smi boundary
     var bigNum = (1 << 30) - 3;
     assertEquals(bigNum + 7, new Array(bigNum).unshift(1, 2, 3, 4, 5, 6, 7));
   }
 })();
+
+(function() {
+  for (var i = 0; i < 7; i++) {
+    var a = [6, 7, 8, 9];
+    a.unshift(1, 2, 3, 4, 5);
+    assertEquals([1, 2, 3, 4, 5, 6, 7, 8, 9], a);
+  }
+})();