This is a reland of dbdede01
after a webkit layout test (geolocation-api/timestamp.html) was
fixed by
https://chromium-review.googlesource.com/c/chromium/src/+/994343 .

Original change's description:
> Implement a new spec for timezone offset calculation
>
> https://github.com/tc39/ecma262/pull/778 was recently merged
> to Ecma 262.
>
> It changes the way to convert between "local time" and UTC in such
> a way that it'd work for all timezones whether or not there has
> been any change in the timezone offset of the standard time. For
> instance, Europe/Moscow and some parts of US state of Indiana have
> changed the standard (non-DST) timezone offset a few times. The
> previous spec assumes that the the standard timezone offset is
> constant, but the new spec take into account the offset change
> history.
>
> In addition, it specifies a new way to calculate the timezone
> offset during a timezone transition (either in and
> out of DST or timezone offset shift).
>
> During a negative transition (e.g.  fall backward / getting
> out of DST), repeated times are to be interpreted as if the
> offset before the transition is in effect.
>
> During a positive transition (e.g. spring forward / getting
> into DST), skipped times are to be treated similarly. That
> is, they are to be interpreted as if the offset before the
> transition is in effect.
>
> With icu-timezone-data, v8 is compliant to the new spec for the
> past and the future as well as now whether or not the standard
> timezone offset of a given timezone has changed over time
> (e.g. Europe/Moscow, Pacific/Apia). With icu-timezone-data,
> Australia/Lord_Howe (30 minute DST change) also works per spec.
>
> Without icu-timezone-data, it works only for timezones of which
> the standard timezone offset is the same as the current offset
> (e.g. most North American timezones other than parts of Indiana)
> and of which the DST shift is an hour. For instance, it doesn't work
> for Europe/Moscow in 2010 when the standard timezone offset was
> +4h because the current (2018) standard timezone offset is +3h. Neither
> does it for Lord Howe in Australia with the DST shift of 0.5 hr.
>
> This CL used to require one of the two ICU CLs below, but not
> any more.
>
>   https://chromium-review.googlesource.com/c/chromium/deps/icu/+/572652
>   https://chromium-review.googlesource.com/851265  (a proposed CL to the
>   upstream ICU).
>
> Bug: v8:3547,chromium:417640,v8:5714
> Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng
> Change-Id: Ib162295da5bee31b2390bd0918157014aebd3e33
> Reviewed-on: https://chromium-review.googlesource.com/572148
> Commit-Queue: Jungshik Shin <jshin@chromium.org>
> Reviewed-by: Daniel Ehrenberg <littledan@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#52332}

Bug: v8:3547, chromium:417640, v8:5714
Change-Id: I47536c111143f75e3cfeecf5d9761c43a98a10f5
Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng;master.tryserver.blink:linux_trusty_blink_rel
Reviewed-on: https://chromium-review.googlesource.com/995971
Commit-Queue: Jungshik Shin <jshin@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52372}