Fake selection is updated regardless of whether it needs to be updated

[Reinmar]

During image resizing the renderer is executed on every change of the image (I'm not sure who triggers the renderer, but it happens, and it just may happen, so let's accept this fact).

Unfortunately, the renderer doesn't check whether fake selection really needs to be updated so on every call it removes the native selection and sets it back in the same place.

This causes serious deoptimization – Chrome blocks rendering thread for a long periods, stacking some selection changes. It only renders (probably) when for a certain period of time it doesn't get any selection change.

[Reinmar]

Look how long this frame is and what's happening at the end of it:

By inspecting this frame's content we realised that those selection changes may be some sort of blocker for the renderer thread. It's not 100% clear why browser delays rendering, but even though those selection changes are super short, they turned out to be blocking.

After we resolved this issue (with a hack for test purposes) Chrome immediately started to render after every mousemove interaction. Before this fix, there are multiple mousemove per frame.