Throttle resize events during live window resize.
<http://webkit.org/b/114292>
<rdar://problem/13411454>

Reviewed by Geoffrey Garen.

Limit resize events to one at max every 0.2 seconds during live window resize.
This mitigates heavy CPU usage during resize on pages with complex onresize handlers.
If there's a pending resize event when the live resize ends, it fires immediately.

* page/FrameView.cpp:
(WebCore::FrameView::sendResizeEvent):

    Factored out dispatch of the resize event after layout so we can call it on a timer
    instead of immediately while live window resize is active.

(WebCore::FrameView::FrameView):
(WebCore::FrameView::performPostLayoutTasks):
(WebCore::FrameView::delayedResizeEventTimerFired):
(WebCore::FrameView::willEndLiveResize):
(WebCore::FrameView::scheduleResizeEvent):
* page/FrameView.h:
* platform/ScrollableArea.h:

    Made willStartLiveResize() and willEndLiveResize() virtual so we can override
    them on FrameView.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@148031 268f45cc-cd09-0410-ab3c-d52691b4dbfc