Merge up to 8597 to experimental/gc from the bleeding edge.

test/mjsunit/unbox-double-arrays.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 58 matching lines @@
 foo2[25] = new Object();
 for (var i= 0; i < 100000; i += 500 ) {
   if (i != 25 && i != 5) {
     assertEquals(i+0.5, foo2[i]);
   }
 }
 assertTrue(undefined === foo2[5])
 assertTrue(undefined === foo2[500000-1])
 assertTrue(undefined === foo2[-1])
 assertEquals(500000, foo2.length);