This is a reland of c71fd20c
Original change's description:
> [wasm] Data structures for JIT-ing wasm to native memory.
>
> This CL introduces the structures for JIT-ing wasm on the native heap.
> They are described in detail at go/wasm-on-native-heap-stage-1
>
> Briefly:
> - WasmCodeManager manages memory for modules and offers an interior
> pointer lookup (i.e. PC -> WasmCode)
> - WasmCode represents code, including reloc info. It holds wasm
> specific data, like function index, and runtime information, like trap
> handler info.
> - NativeModule manages memory for one module.
>
> Tests cover the allocation and lookup aspects, following that current
> regression tests cover the JITed code. A separate CL will enable
> JITing using the new data structures.
>
> Bug: v8:6876
> Change-Id: I1731238409001fe97c97eafb7a12fd3922da6a42
> Reviewed-on: https://chromium-review.googlesource.com/767581
> Commit-Queue: Mircea Trofin <mtrofin@chromium.org>
> Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
> Reviewed-by: Ben Titzer <titzer@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#49501}

Bug: v8:6876
Change-Id: Ifd1a4c23de8150dbdc75f059cd657e9670b15c9b
Reviewed-on: https://chromium-review.googlesource.com/779680
Commit-Queue: Mircea Trofin <mtrofin@chromium.org>
Reviewed-by: Brad Nelson <bradnelson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49512}