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}