LibWeb: Use PaintableBox::is_scrollable() while dispatching wheel event

With this change we use the same function to determine whether to render
scroll thumb and whether box wants to accept scroll UI events.

Userland/Libraries/LibWeb/Layout/Box.cpp

@@ -60,12 +60,6 @@ bool Box::is_scroll_container() const
         || overflow_value_makes_box_a_scroll_container(computed_values().overflow_y());
 }
 
-bool Box::is_user_scrollable() const
-{
-    // FIXME: Support horizontal scroll as well (overflow-x)
-    return computed_values().overflow_y() == CSS::Overflow::Scroll || computed_values().overflow_y() == CSS::Overflow::Auto;
-}
-
 bool Box::is_body() const
 {
     return dom_node() && dom_node() == document().body();

Userland/Libraries/LibWeb/Layout/Box.h

@@ -52,8 +52,6 @@ public:
 
     bool is_scroll_container() const;
 
-    bool is_user_scrollable() const;
-
     void add_contained_abspos_child(JS::NonnullGCPtr<Node> child) { m_contained_abspos_children.append(child); }
     void clear_contained_abspos_children() { m_contained_abspos_children.clear(); }
     Vector<JS::NonnullGCPtr<Node>> const& contained_abspos_children() const { return m_contained_abspos_children; }

Userland/Libraries/LibWeb/Painting/PaintableBox.cpp

@@ -775,12 +775,9 @@ Paintable::DispatchEventOfSameName PaintableBox::handle_mousemove(Badge<EventHan
 
 bool PaintableBox::handle_mousewheel(Badge<EventHandler>, CSSPixelPoint, unsigned, unsigned, int wheel_delta_x, int wheel_delta_y)
 {
-    if (!layout_box().is_user_scrollable())
-        return false;
-
-    // TODO: Vertical and horizontal scroll overflow should be handled seperately.
-    if (!has_scrollable_overflow())
+    if (!is_scrollable()) {
         return false;
+    }
 
     scroll_by(wheel_delta_x, wheel_delta_y);
     return true;