Created attachment 95408 [details]
testcase

Compile with 
gcc `pkg-config WebKitGdk gtk+-2.0 glib-2.0 --cflags --libs` main.cpp testcase-embed.h testcase-embed.cpp

Ok, I know what happens. GtkScrolledWindow uses gtk_widget_get_child_requisition to get the size of the scrollbars in size_allocate, so it assumes that size_request was called before (otherwise the values there will be outdated). Seems we are not doing this anywhere but once on startup, so from that point we live with width/height 0 for the scrollbars. I suppose this didn't matter on mozilla because the scrollbars are not real widgets there.

Patch to fix this follows.

Created attachment 96404 [details] [review]
[1/1] Implement size_request for EphyTab.

 src/ephy-tab.c |   19 +++++++++++++++++++
 1 files changed, 19 insertions(+), 0 deletions(-)

Committed on trunk.