Replaces deprecated CFGregorianDate with CFCalendar.

Several CFGregorianDate APIs have been deprecated starting in iOS8.
Use CFCalendar APIs instead.

Keep separate implementation on Mac and iOS as base/time/time_posix.cc
does not work on 32-bit architecture on Mac or iOS, and even though Mac
is only build in 64-bit, iOS still support both architectures.

BUG=567983

Review URL: https://codereview.chromium.org/1494083005

Cr-Commit-Position: refs/heads/master@{#375438}
1 file changed