WebContent: Use available size for bitmap (#2701)

After adding the scrolling feature, content available space reduced and
thus the bitmap size was always larger, than the inner size.
This lead to the horizontal scrollbar always beeing engaged.

Demos/WebView/WebContentView.cpp

@@ -48,7 +48,7 @@ void WebContentView::load(const URL& url)
 
 void WebContentView::paint_event(GUI::PaintEvent& event)
 {
-    GUI::Frame::paint_event(event);
+    GUI::ScrollableWidget::paint_event(event);
 
     GUI::Painter painter(*this);
     painter.add_clip_rect(frame_inner_rect());
@@ -61,11 +61,12 @@ void WebContentView::paint_event(GUI::PaintEvent& event)
 
 void WebContentView::resize_event(GUI::ResizeEvent& event)
 {
-    GUI::Widget::resize_event(event);
-    auto bitmap = Gfx::Bitmap::create(Gfx::BitmapFormat::RGB32, event.size());
+    GUI::ScrollableWidget::resize_event(event);
+
+    auto bitmap = Gfx::Bitmap::create(Gfx::BitmapFormat::RGB32, available_size());
     m_bitmap = bitmap->to_bitmap_backed_by_shared_buffer();
     m_bitmap->shared_buffer()->share_with(client().server_pid());
-    client().post_message(Messages::WebContentServer::SetViewportRect(Gfx::IntRect({ horizontal_scrollbar().value(), vertical_scrollbar().value() }, event.size())));
+    client().post_message(Messages::WebContentServer::SetViewportRect(Gfx::IntRect({ horizontal_scrollbar().value(), vertical_scrollbar().value() }, m_bitmap->size())));
     request_repaint();
 }
 
@@ -116,7 +117,7 @@ void WebContentView::notify_server_did_change_title(Badge<WebContentClient>, con
 
 void WebContentView::did_scroll()
 {
-    client().post_message(Messages::WebContentServer::SetViewportRect(Gfx::IntRect({ horizontal_scrollbar().value(), vertical_scrollbar().value() }, size())));
+    client().post_message(Messages::WebContentServer::SetViewportRect(visible_content_rect()));
     request_repaint();
 }