DevTools: Speedup flamechart window scrolling

There's no need to call _updateSelectedRangeStats() from TimelinePanel._onWindowChanged
as another call has already been made via:
(TimelineFlameChart|TimelineView).setWindowTimes
TimelinePanel.select
TimelinePanel._updateSelectionDetails

Review URL: https://codereview.chromium.org/361223002

git-svn-id: svn://svn.chromium.org/blink/trunk@177451 bbb929c8-8fbe-4397-9dbb-9b2b20218538