Use AllocationSite without Weaknext field for all the allocations in nested
literal except for Root. The nested field is sufficient to link all the
allocations in a nested literal. Only the Root is added to heap weak_alloc_list
for GC to traverse

Change-Id: I946e63292c6d168197cd2a087f697c73cc431272
Reviewed-on: https://chromium-review.googlesource.com/1101323
Commit-Queue: Chandan Reddy <chandanreddy@google.com>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53813}