Fix ASSERT by reordering the initialization of the arguments boilerplate.

Fix assert by reordering the initialization of the arguments boilerplate.

If a GC happened during initialization (when allocating the elements array)
of the non_strict_arguments_boilerplate, heap verification would fail with the following assert:

ASSERT_EQ((map()->has_fast_elements() || map()->has_fast_smi_only_elements()),
            (elements()->map() == GetHeap()->fixed_array_map() ||
             elements()->map() == GetHeap()->fixed_cow_array_map()));

This was not harmful since the boilerplate was setup 
correctly immediatly afterwards.


Simplified the setup code by removing a call to GetElementsTransitionMap. It always return the same map as 
the input object in this case and is therefore unnecessary.


Added more assertions to verify well-formed non-strict
arguments backing store.

BUG=v8:1520
TEST=no more flaky tests with failing this assert.
 
Committed: http://code.google.com/p/v8/source/detail?r=9678

[Vyacheslav Egorov (Chromium), 2011-10-18 11:11:27]

LGTM