Remove the is_nested bit from the BlockInfo structure.

This will allow us to increase the size of the |body_size| field of the
BlockHeader structure (to handle the allocations > 1GB).

We're not using this feature anyway so it's adding some unneeded complexity to our codebase.

R=chrisha@chromium.org

Review URL: https://codereview.chromium.org/2508333002 .
19 files changed