Web Inspector: extract common base for 3 timeline overview controls (Events/Frames/Memory)
https://bugs.webkit.org/show_bug.cgi?id=113572

Reviewed by Yury Semikhatsky.

Refactoring, covered by existing tests.

- introduce TimelineOverviewBase as a common base for 3 overview controls;
- make every overview control a view.

This does not yet take advantage of common base (subject of the next patch).

* inspector/front-end/OverviewGrid.js:
(WebInspector.OverviewGrid.prototype.gridElement):
(WebInspector.OverviewGrid.prototype.itemsGraphsElement):
* inspector/front-end/TimelineOverviewPane.js:
(WebInspector.TimelineOverviewPane):
(WebInspector.TimelineOverviewPane.prototype.setMode):
(WebInspector.TimelineOverviewPane.prototype._update):
(WebInspector.TimelineOverviewBase):
(WebInspector.TimelineOverviewBase.prototype.update):
(WebInspector.TimelineMemoryOverview):
(WebInspector.TimelineEventOverview):
(WebInspector.TimelineEventOverview.prototype._renderBar):
(WebInspector.TimelineFrameOverview):
(WebInspector.TimelineFrameOverview.prototype.update):
(WebInspector.TimelineFrameOverview.prototype._renderBars):
(WebInspector.TimelineFrameOverview.prototype._drawFPSMarks):
(WebInspector.TimelineFrameOverview.prototype._renderBar):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@147220 268f45cc-cd09-0410-ab3c-d52691b4dbfc