TimelinePanel: REGRESSIONS: three fixes for TimelineOverviewPane.

1) Selected window doesn't slide while recording. Why: there used to be a call for _updateWindow from _update method.
2) No overview for Events mode. Why: raw records may have no valid endTime.
3) The window selection is dropping by recording timeline. Why: earlier overview pane saved the selected time range at _onWindowChanged.

BUG=
R=pfeldman@chromium.org

Review URL: https://codereview.chromium.org/185543012

git-svn-id: svn://svn.chromium.org/blink/trunk@168367 bbb929c8-8fbe-4397-9dbb-9b2b20218538