fixed_gtk_widget_size_allocate is called a lot

[joakim]

I'm debugging some flicker when displaying a gtk socket in the xwidget
branch. Other widgets types don't flicker.

during debugging I find my local override
emacs_fixed_gtk_widget_size_allocate gets called a lot, like during
every redisplay or something. The flickering have the same sort of
frequency. Should gtk widgets allocation happen that often?

Sockets around a bit different from other types of widgets since they
always are native windows, which ordinary widgets aren't by default in GTK3.
-- 
Joakim Verona