Proposal: reuse the same EffectiveViewportChangedEventArgs object

[FrayxRulez]

Currently, every time EffectiveViewportChanged is fired, a new EffectiveViewportChangedEventArgs is created.
While this is probably fine in C++, it causes a huge memory traffic in C# and consequently a large amount of garbage collections.
I see from the source code that quite a few events reuse the same args over and over for performance reasons (ListView.ContainerContentChanging to mention one), and I guess it would make sense to do it here too, as EffectiveViewportChanged callbacks tend to be a hot path (tracking visible elements on screen in scrollable areas and such).

[codendone]

Note: We frequently can't reuse event args because event handlers may be asynchronous and holding on to the args. Some tricks could potentially be done, like using a pool and watching for when the event args are no longer in use.

[FrayxRulez]

Judging from CLayoutManager::RaiseEffectiveViewportChangedEvents it seems possible to at least recycle the same args per queue batch (Raise is being invoked with fRaiseSync TRUE)