This is a reland of d8f564ea

TBR=mstarzinger@chromium.org,yangguo@chromium.org,jgruber@chromium.org

Original change's description:
> Reland: Remove SFI code field
>
> Remove the SharedFunctionInfo code field, inferring the code object
> from the function_data field instead. In some cases, the function_data
> field can now hold a Code object (e.g. some WASM cases).
>
> (Reland of https://chromium-review.googlesource.com/952452)
>
> TBR=mstarzinger@chromium.org
>
> Bug: chromium:783853
> Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng
> Change-Id: I10ea5be7ceed1b51362a2fad9be7397624d69343
> Reviewed-on: https://chromium-review.googlesource.com/970649
> Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> Reviewed-by: Yang Guo <yangguo@chromium.org>
> Reviewed-by: Jakob Gruber <jgruber@chromium.org>
> Reviewed-by: Leszek Swirski <leszeks@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#52136}

Bug: chromium:783853
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I5187851b923e9a92f43daf8cb99e662786cbb839
Reviewed-on: https://chromium-review.googlesource.com/975942
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52159}