This reverts commit ae9a2d38.

Reason for revert: Regresses benchmarks related to maps and sets. 
Regressions here: https://chromeperf.appspot.com/group_report?rev=46756.
In future when we move these builtins to CSA, we may still want to
remove this flag.

Original change's description:
> Remove SetForceInlineFlag from src/js/*
> 
> Remove SetForceInlineFlag from the js builtins. 
> 
> Bug: 
> Change-Id: I962982509c82e4baba8dc32a0f163147c47daf34
> Reviewed-on: https://chromium-review.googlesource.com/571803
> Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
> Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
> Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
> Commit-Queue: Mythri Alle <mythria@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#46756}

TBR=rmcilroy@chromium.org,jarin@chromium.org,mythria@chromium.org,bmeurer@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I96651aa9d6e91e593af8da1b531e9f7b0240088f
Reviewed-on: https://chromium-review.googlesource.com/579194
Commit-Queue: Mythri Alle <mythria@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Mythri Alle <mythria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46797}