Drag handlers positioning coalescing

[xmo]

Working on a 4.3-based system using widgets, I recently started looking into the performances of starting the editor to see if it'd be possible to speed it up.

In my "test case" (a page of the system), CKEDITOR.inline is called on a page section holding 1300 nodes, including 46 would-be widget.

Looking at the Chrome timeline (frames section), I noticed that within CKEDITOR's "readiness" handler (a timer in scriptloader), there's a significant sequence of layout recomputations which Chrome marks with a warning (it's a whole-document synchronous operation).

The issue here is that positionDragHandler accesses offsetTop and offsetLeft which requires a valid layout, but the setup of each widget invalidates the layout by setting a bunch classes & attributes on it. Which means the layout must be entirely recomputed during each positionDragHandler, aka once per widget.

Coalescing the calls (by setting up a timeout, adding widgets to a queue then running the actual positionDragHandler on all widgets at once) saves about 100ms between the call to CKEDITOR.inline and the triggering of instanceReady (~1400ms -> ~1300ms) on a 15" 2010 MBP, under Chrome 29. It also makes the timeline significantly cleaner.

[Piotrek Koszuliński]

Thanks for feedback on this. Have you noticed any other operations done during widgets initialization which force reflow?

[xmo]

Nothing stands out in the timeline, but I haven't dug much further yet.

[Piotrek Koszuliński]

Related ticket: #11161.

[Marek Lewandowski]

Issue will be fixed by #11161.

[Marek Lewandowski]

Fixed in #11177 with ​git:32e096f4fb70