scrolledwindow: Bug 766569 - Report child natural size unconditionally

This patch causes the scrolled window default behavior to change in
such a way that the natural size request of the child is unconditionally
reported, which probably should have been the case since day 1.

This should not cause significant fallout since a scrolled window is
normally used to expand/fill, eating up remaining space for scrollable
content - it will however cause the scrolled window to compete for
additional space with siblings, proportionally to the size of the
scrolled window's content.

gtk/gtkscrolledwindow.c

@@ -1781,17 +1781,18 @@ gtk_scrolled_window_measure (GtkCssGadget   *gadget,
                                           &min_child_size,
                                           &nat_child_size);
 
+	  natural_req.width += nat_child_size;
+
 	  if (priv->hscrollbar_policy == GTK_POLICY_NEVER)
 	    {
 	      minimum_req.width += min_child_size;
-	      natural_req.width += nat_child_size;
 	    }
 	  else
 	    {
 	      if (priv->min_content_width >= 0)
 		{
 		  minimum_req.width += priv->min_content_width;
-		  natural_req.width += priv->min_content_width;
+		  natural_req.width  = MAX (priv->min_content_width, natural_req.width);
 		  extra_width = -1;
 		}
 
@@ -1822,17 +1823,18 @@ gtk_scrolled_window_measure (GtkCssGadget   *gadget,
                                            &min_child_size,
                                            &nat_child_size);
 
+	  natural_req.height += nat_child_size;
+
 	  if (priv->vscrollbar_policy == GTK_POLICY_NEVER)
 	    {
 	      minimum_req.height += min_child_size;
-	      natural_req.height += nat_child_size;
 	    }
 	  else
 	    {
 	      if (priv->min_content_height >= 0)
 		{
 		  minimum_req.height += priv->min_content_height;
-		  natural_req.height += priv->min_content_height;
+		  natural_req.height  = MAX (priv->min_content_height, natural_req.height);
 		  extra_height = -1;
 		}