This way, we also ensure that timeGetTime() is used for Time::Now(),
and thereby Date.now() even if GetTickCount64() is available.

Also add test coverage for Time::Now(), TimeTicks::Now() and
TimeTicks::HighResNow().

BUG=chromium:288924
TEST=cctest/test-timer
R=hpayer@chromium.org

Review URL: https://codereview.chromium.org/25468003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@17080 ce2b1a6d-e550-0410-aec6-3dcde31c8c00