TimelinePanel: move conversion from OverviewGrid window to windowTimes to TimelineOverviewPane

This patch reduces the dependency between TimelineView and _overviewConroller
which is an instance of TimelineOverviewBase successor.

BUG=326121
R=caseq@chromium.org

Review URL: https://codereview.chromium.org/148173004

git-svn-id: svn://svn.chromium.org/blink/trunk@165933 bbb929c8-8fbe-4397-9dbb-9b2b20218538