Use TimeDelta in Scrollbar/ScrollableArea/ScrollbarTheme

Straightforward conversion in Scrollbar and ScrollableArea.

In ScrollbarTheme, OverlayScrollbarFadeOutDelaySeconds,
OverlayScrollbarFadeOutDurationSeconds, InitialAutoscrollTimerDelay and
AutoscrollTimerDelay are changed to return TimeDelta. The "Seconds"
suffix is dropped from the two earlier methods.

Bug: 763980
Change-Id: Idf1a8b1e44db18427db7a9acebd09f63be2c4cdc
Reviewed-on: https://chromium-review.googlesource.com/1127781
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573274}
16 files changed