Use TimeDelta in PausableTimer

Mostly s/double/TimeDelta/ and Method() to MethodDelta(). The
kNextFireIntervalInvalid constant is changed to TimeDelta::Min().

Bug: 763980
Change-Id: I878a4136edcfe815184e7021a19eefffbc02fd31
Reviewed-on: https://chromium-review.googlesource.com/1125919
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#572612}
2 files changed