Use a single FlGLArea

[robert-ancell]

Further simplification from #39467

[flutter-dashboard]

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[robert-ancell]

@jpnurmi please try this and see if it resolved your first frame issue.

[robert-ancell]

Fast clicking and dragging on the (+) button is causing crashes with this branch, which don't seem reproducible with the previous branches.

[robert-ancell]

The crashes seem to be related to getting leave events after releasing the button. I don't know why GTK is taking focus away :/

[jpnurmi]

Thanks! I'm no longer able to reproduce the blank window issue with this.

[robert-ancell]

Fixed crash, should be good to review once #39467 is landed.

[flutter-dashboard]

This pull request executed golden file tests, but it has not been updated in a while (20+ days). Test results from Gold expire after as many days, so this pull request will need to be updated with a fresh commit in order to get results from Gold.

[cbracken]

Looks like this will need to be rebased to tip-of-tree to deal with a few conflicts.

[cbracken]