Timeline: move overviewControl into TimelineView part of TimelinePanel

This change unblock another change that breaks the dependency of TimelineView from TimelineOverviewPane.
In that change I'll replace calls like this._overviewPane.windowStartTime() with this._windowStartTime

BUG=
R=caseq@chromium.org

Review URL: https://codereview.chromium.org/117093003

git-svn-id: svn://svn.chromium.org/blink/trunk@164087 bbb929c8-8fbe-4397-9dbb-9b2b20218538