Reason for revert:
Invalid DCHECKs for non-matched groups.
Original issue's description:
> [regexp] Named capture support for string replacements
>
> This implements support for named captures in
> RegExp.prototype[@@replace] for when the replaceValue is not callable.
>
> Named captures can be referenced from replacement strings by using the
> "$<name>" syntax. A couple of examples:
>
> let re = /(?<fst>.)(?<snd>.)/u;
> "abcd".replace(re, "$<snd>$<fst>") // "bacd"
> "abcd".replace(re, "$2$1") // "bacd" (numbered refs work as always)
> "abcd".replace(re, "$<snd") // SyntaxError (unterminated named ref)
> "abcd".replace(re, "$<42$1>") // "cd" (invalid name)
> "abcd".replace(re, "$<thd>") // "cd" (non-existent name)
> "abcd".replace(/(?<fst>.)|(?<snd>.)/u, "$<snd>") // "cd" (non-matched capture)
>
> Support is currently behind the --harmony-regexp-named-captures flag.
>
> BUG=v8:5437
>
> Review-Url: https://codereview.chromium.org/2775303002
> Cr-Commit-Position: refs/heads/master@{#44171}
> Committed: 17f13863b6TBR=yangguo@chromium.org,littledan@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:5437
Review-Url: https://codereview.chromium.org/2776293003
Cr-Commit-Position: refs/heads/master@{#44180}
34ffdd6238