getting the requested size of a widget

[Julian Bradfield <jcb+gtk-app-devel inf ed ac uk>]

How do I get a widget to tell me truly how much size it would like?
gtk_widget_size_request does not appear to work.

Specifically, I have a dialog window that contains a notebook with
five pages; each page contains a textview wrapped in a scrolledwindow.
Some information arrives, I stuff it into the relevant pages, and then
pop up the dialog.
However, I would like the dialog to ask the window manager for as much
size as is needed to display the largest page without scrolling, not
just the currently selected page.

I thought I could do this by asking the page textview widgets their
size with gtk_widget_size_request, and then using
gtk_widget_set_size_request to tell the selected page to ask for the
maximum of these sizes.

However, the values I get back from gtk_widget_size_request seem
arbitrary. Some of them (usually the first pages to have their text
information updated) seem accurate, but the others are sometimes too
small (e.g (0,19), suggesting a requistion on the basis of no text),
or too large (a screen height or more), for which I have no idea whence it
came.

This is with gtk+ 2.14.4.

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