We need to re-create CompositorWidgetInitData when widget is hidden/shown.

A compositor can be created before we get a gtk widget map event. That leads to wrong XWindow reference passed to GtkCmmpositorWidget.
In this patch we destroy compositor on gtk map event (if there's any) to make sure it's recreated with correct XWindow reference.

try: https://treeherder.mozilla.org/#/jobs?repo=try&revision=20fc1fcb332eb999268959dd22890cda9ba5af3d

The error is: Failed to connect WebRenderBridgeChild

It looks like the CleanLayerManagerRecursive() I use to force re-create compositor is not enough. Looks like there's CompositorBridgeParent left with incorrect mRootLayerTreeID and when another compositor is created, BrowserChild::InitRenderingState() is called with that old mRootLayerTreeID which leads to 'NO_PARENT' error and fallback compositor is created.

That also implies that nsWindow::SetTransparencyMode() may produce the same error:
https://searchfox.org/mozilla-central/rev/81c52abeec336685330af5956c37b4bcf8926476/widget/gtk/nsWindow.cpp#6384

There's a r+ patch which didn't land and no activity in this bug for 2 weeks.
:stransky, could you have a look please?
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try: https://treeherder.mozilla.org/#/jobs?repo=try&revision=c76ecbf992dd8abed246f31cbfe87b0527a49a9a

We can't do that - resume is enough here and that's in Bug 1777664.