LibWeb+LibWebView+Ladybird: Scale scroll-to CSS positions in PageHost

The `page_did_request_scroll_to` API takes a CSS position, and thus
callers should not scale to device pixels before invoking it. Instead,
align this API with (most) other PageHost APIs which scale to device
pixels before sending the corresponding IPC message.

In the AppKit chrome, convert the provided device pixel position to a
widget position.

Ladybird/AppKit/UI/LadybirdWebView.mm

@@ -279,7 +279,7 @@ static void copy_data_to_clipboard(StringView data, NSPasteboardType pasteboard_
         [self.observer onFaviconChange:bitmap];
     };
 
-    m_web_view_bridge->on_scroll_to_point = [self](auto position) {
+    m_web_view_bridge->on_scroll = [self](auto position) {
         auto content_rect = [self frame];
         auto document_rect = [[self documentView] frame];
         auto ns_position = Ladybird::gfx_point_to_ns_point(position);

Ladybird/AppKit/UI/LadybirdWebViewBridge.cpp

@@ -38,7 +38,7 @@ WebViewBridge::WebViewBridge(Vector<Gfx::IntRect> screen_rects, float device_pix
     create_client(WebView::EnableCallgrindProfiling::No);
 
     on_scroll_by_delta = [this](auto x_delta, auto y_delta) {
-        auto position = to_widget_position(m_viewport_rect.location());
+        auto position = m_viewport_rect.location();
         position.set_x(position.x() + x_delta);
         position.set_y(position.y() + y_delta);
 
@@ -63,6 +63,11 @@ WebViewBridge::WebViewBridge(Vector<Gfx::IntRect> screen_rects, float device_pix
         if (on_scroll_to_point)
             on_scroll_to_point(position);
     };
+
+    on_scroll_to_point = [this](auto position) {
+        if (on_scroll)
+            on_scroll(to_widget_position(position));
+    };
 }
 
 WebViewBridge::~WebViewBridge() = default;

Ladybird/AppKit/UI/LadybirdWebViewBridge.h

@@ -56,6 +56,7 @@ public:
     Optional<Paintable> paintable();
 
     Function<void()> on_zoom_level_changed;
+    Function<void(Gfx::IntPoint)> on_scroll;
 
 private:
     WebViewBridge(Vector<Gfx::IntRect> screen_rects, float device_pixel_ratio, Optional<StringView> webdriver_content_ipc_path, Web::CSS::PreferredColorScheme);

Userland/Libraries/LibWeb/DOM/Element.cpp

@@ -1669,8 +1669,7 @@ static ErrorOr<void> scroll_an_element_into_view(DOM::Element& target, Bindings:
 
             // AD-HOC:
             auto* page = document.navigable()->traversable_navigable()->page();
-            auto scale = page->client().device_pixels_per_css_pixel();
-            page->client().page_did_request_scroll_to({ position.left() * scale, position.top() * scale });
+            page->client().page_did_request_scroll_to(position.location());
         }
         // If scrolling box is associated with an element
         else {

Userland/Services/WebContent/PageHost.cpp

@@ -257,7 +257,8 @@ void PageHost::page_did_request_scroll(i32 x_delta, i32 y_delta)
 
 void PageHost::page_did_request_scroll_to(Web::CSSPixelPoint scroll_position)
 {
-    m_client.async_did_request_scroll_to({ scroll_position.x().to_int(), scroll_position.y().to_int() });
+    auto device_scroll_position = page().css_to_device_point(scroll_position);
+    m_client.async_did_request_scroll_to(device_scroll_position.to_type<int>());
 }
 
 void PageHost::page_did_request_scroll_into_view(Web::CSSPixelRect const& rect)