This is a reland of a0c57368

Original change's description:
> [wasm] Maintain link from Instance to Module.
> 
> This moves the link from a {WasmInstanceObject} to its corresponding
> {WasmModuleObject} into the right place and also makes it strong. This
> ensures that an instance always keeps the underlying module alive and
> hence removes the situation of an "orphaned instance".
> 
> R=clemensh@chromium.org
> 
> Change-Id: Id59f6a49740af8ef0248679c3d2c696bb9776944
> Reviewed-on: https://chromium-review.googlesource.com/1041691
> Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
> Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#52942}

Change-Id: I9854400bfc1d22bd258f17118fcb7460cdc3acd5
Reviewed-on: https://chromium-review.googlesource.com/1043786Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52985}