This is a reland of 6d5b54df82e27a82811a836dcdbbfe26829f0e6d
Original change's description:
> [cleanup] Harden the SubString CSA/Runtime implementations.
>
> Remove the self-healing for invalid parameters in the
> CodeStubAssembler::SubString helper and the %SubString runtime function,
> which is used as a fallback for the CodeStubAssembler implementation.
> All call sites must do appropriate parameter validation anyways now that
> the self-hosted JavaScript builtins using these helpers are gone, and we
> have proper contracts with the uses.
>
> Also remove the context parameter from the CodeStubAssembler::SubString
> method, which is unnecessary, since this can no longer throw an
> exception.
>
> Bug: v8:5269, v8:6936, v8:7109, v8:7137
> Change-Id: I19d93bad5f41faa0561c4561a48f78fcba99a549
> Reviewed-on: https://chromium-review.googlesource.com/795720
> Reviewed-by: Jakob Gruber <jgruber@chromium.org>
> Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#49702}

Bug: v8:5269, v8:6936, v8:7109, v8:7137
Change-Id: I5e84998a2dd3990d7981505b401ffc770e0b7ac5
Reviewed-on: https://chromium-review.googlesource.com/913130Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51265}