Make the FrameLayerBuilder remember for what region it has calculated
display item visibility, then recompute the visibility whenever the
dirty region it is passed to DrawPaintedLayer changes.
This means that the caller does not have to know the entire dirty region
that will be drawn for the transaction, but we can still optimise cases
where it knows some of the dirty region in advance.
This fixes a regression where MultiTiledContentClient's low-res display
port would not be painted if a smaller region of its high-res buffer had
already been painted that transaction, since the FrameLayerBuilder
had decided that most of the larger low-res region was invisible.
The high-level overview is that the parts of nsWebBrowserPersist which
access the DOM have been factored out (as WebBrowserPersistLocalDocument)
and abstracted (nsIWebBrowserPersistDocument) such that they can be
implemented in the cross-process case using IPC.
Bug 1176077 introduced the parameter aDirtyRegion to
DrawPaintedLayerCallback, which allows the callback to recompute the
visibility of all items to be painted in that transaction in a single
go. However, this parameter can not always be determined correctly
when using RotatedBuffer, and using an incorrect value was causing
graphical glitches.
Make the parameter optional, and on null values do not perform the
optimisation. Pass null from ClientPaintedLayer, which uses
RotatedBuffer and was causing problems, but continue to pass the
correct value from other Layer implementations. This optimisation was
most important for tiled layers using progressive paint, so this is
okay.
FrameLayerManager::RecomputeItemsVisibility() was being called on every
call to FrameLayerBuilder::DrawPaintedLayer(), each time for the region
to be painted by that paint call. This is inefficient when progressive
paint is enabled. Change it so that we compute the visibility of all the
layer's items within the total region to be painted, but only on the
first paint after the display list has been modified.
