convert BitVector to use pointer size blocks

test/cctest/test-dataflow.cc

 // Copyright 2012 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 65 matching lines @@
     w.Add(1);
     v.Union(w);
     CHECK(v.Contains(0));
     CHECK(v.Contains(1));
   }
 
   {
     BitVector v(15, &zone);
     v.Add(0);
     BitVector w(15, &zone);
-    w = v;
+    w.CopyFrom(v);
     CHECK(w.Contains(0));
     w.Add(1);
     BitVector u(w, &zone);
     CHECK(u.Contains(0));
     CHECK(u.Contains(1));
     v.Union(w);
     CHECK(v.Contains(0));
     CHECK(v.Contains(1));
   }
 
@@ skipping 15 matching lines @@
     w.Add(33);
     v.Intersect(w);
     CHECK(!v.Contains(32));
     CHECK(v.Contains(33));
     BitVector r(35, &zone);
     r.CopyFrom(v);
     CHECK(!r.Contains(32));
     CHECK(r.Contains(33));
   }
 }