If animations are disabled, the only difference we need to make is that
we don't have to start the transition. Size requests should remain the
same.
https://bugzilla.gnome.org/show_bug.cgi?id=762996
... if the child is concealed and the transition type is set to NONE.
In this case, both preferred width and preferred height should be 0, but
we still can't use that to allocate a size for the child, so care about
the minimum size of the child in gtk_revealer_get_child_allocation.
https://bugzilla.gnome.org/show_bug.cgi?id=761760
These days exposure happens only on the native windows (generally the
toplevel window) and is propagated down recursively. The expose event
is only useful for backwards compat, and in fact, for double buffered
widgets we totally ignore the event (and non-double buffering breaks
on wayland).
So, by not setting the mask we avoid emitting these events and then
later ignoring them.
We still keep it on eventbox, fixed and layout as these are used
in weird ways that want backwards compat.
When animation is disabled, we use 'none' as the effective
transition type. So far, this transition type failed to change
the size request, causing the revealer to always take up the
space of the child, even when the child is not shown.
https://bugzilla.gnome.org/show_bug.cgi?id=719568
-Avoid defining variables in the middle of the block
-Include fallback-c89.c in gtkrevealer.c in place of math.h as
fallback-c89.c includes math.h itself, and is needed for round()
