don't display search popover while animating search bar
animating the popover while also animating the searchbar (search-mode-enabled) results in a bunch of missed frames. its simply too much to do at once.
I suggest not displaying the popover until after the search-mode-enabled animation has completed.
Alternatively, it might be worth considering not showing the popover at all until text is inserted to the GtkSearchEntry. As with Builder previously, I'm not sure how useful the popover is with just "type to search" text.
I haven't tested with master yet, just whatever is on F22, so sorry if things have changed!