This is a reland of 380dba0a

Original change's description:
> [runtime][gc] Drop AllocationSite::weak_next field for sub-literals
> 
> 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}

Change-Id: Ic451fb3600b87f8f69748b1659ff89a80c9322fa
Reviewed-on: https://chromium-review.googlesource.com/1106257Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Chandan Reddy <chandanreddy@google.com>
Cr-Commit-Position: refs/heads/master@{#53872}