Looking at the Totem code, it looks like a set of GktButtons inside a GtkToolbar, with a CSS style applied and using symbolic icons (which are also installed by the theme in Ubuntu) instead of the stock ones.
Here's an example in Python
# Assuming builder is an initialized Gtk.Builder object and toolbar exists
# in the .ui definition file and is populated with Gtk.ToolButtons
context = builder.get_object('toolbar').get_style_context()
context.add_class(Gtk.STYLE_CLASS_INLINE_TOOLBAR)
Looking at the Totem code, it looks like a set of GktButtons inside a GtkToolbar, with a CSS style applied and using symbolic icons (which are also installed by the theme in Ubuntu) instead of the stock ones.
Here's an example in Python
More info on GTK+ 3 CSS styles:
It is buttons on ".inline-toolbar"..