LibWeb: Implement Screen.isExtended attribute

- Add WindowManagement to PolicyControlledFeature enum
- Add screen_count() virtual method to PageClient
- Store all screen rects in WebContent::PageClient, derive both
  screen_rect() and screen_count() from stored data
- Implement screen_count() overrides in SVGPageClient and PageHost
- Replace FIXME stub in Screen.cpp with spec-compliant implementation

Libraries/LibWeb/CSS/Screen.cpp

@@ -95,8 +95,13 @@ GC::Ref<ScreenOrientation> Screen::orientation()
 // https://w3c.github.io/window-management/#dom-screen-isextended
 bool Screen::is_extended() const
 {
-    dbgln("FIXME: Unimplemented Screen::is_extended");
-    return false;
+    // 1. If this's relevant global object's associated Document is not allowed to use
+    //    the policy-controlled feature named "window-management", return false.
+    if (!window().associated_document().is_allowed_to_use_feature(DOM::PolicyControlledFeature::WindowManagement))
+        return false;
+
+    // 2. Return true if the device has more than one screen, and false otherwise.
+    return window().page().client().screen_count() > 1;
 }
 
 // https://w3c.github.io/window-management/#dom-screen-onchange

Libraries/LibWeb/DOM/Document.cpp

@@ -4528,6 +4528,9 @@ bool Document::is_allowed_to_use_feature(PolicyControlledFeature feature) const
     case PolicyControlledFeature::Gamepad:
         // FIXME: Implement allowlist for this.
         return true;
+    case PolicyControlledFeature::WindowManagement:
+        // FIXME: Implement allowlist for this.
+        return true;
     }
 
     // 4. Return false.

Libraries/LibWeb/DOM/Document.h

@@ -176,6 +176,7 @@ enum class PolicyControlledFeature : u8 {
     EncryptedMedia,
     FocusWithoutUserActivation,
     Gamepad,
+    WindowManagement,
 };
 
 class WEB_API Document

Libraries/LibWeb/Page/Page.h

@@ -341,6 +341,7 @@ public:
     virtual CSS::PreferredColorScheme preferred_color_scheme() const = 0;
     virtual CSS::PreferredContrast preferred_contrast() const = 0;
     virtual CSS::PreferredMotion preferred_motion() const = 0;
+    virtual size_t screen_count() const = 0;
     virtual Queue<QueuedInputEvent>& input_event_queue() = 0;
     virtual void report_finished_handling_input_event(u64 page_id, EventResult event_was_handled) = 0;
     virtual void page_did_change_title(Utf16String const&) { }

Libraries/LibWeb/SVG/SVGDecodedImageData.h

@@ -85,6 +85,7 @@ public:
     virtual CSS::PreferredColorScheme preferred_color_scheme() const override { return m_host_page->client().preferred_color_scheme(); }
     virtual CSS::PreferredContrast preferred_contrast() const override { return m_host_page->client().preferred_contrast(); }
     virtual CSS::PreferredMotion preferred_motion() const override { return m_host_page->client().preferred_motion(); }
+    virtual size_t screen_count() const override { return 1; }
     virtual void request_file(FileRequest) override { }
     virtual Queue<QueuedInputEvent>& input_event_queue() override { VERIFY_NOT_REACHED(); }
     virtual void report_finished_handling_input_event([[maybe_unused]] u64 page_id, [[maybe_unused]] EventResult event_was_handled) override { }

Services/WebContent/PageClient.h

@@ -53,7 +53,11 @@ public:
 
     void set_palette_impl(Gfx::PaletteImpl&);
     void set_viewport_size(Web::DevicePixelSize const&);
-    void set_screen_rects(Vector<Web::DevicePixelRect, 4> const& rects, size_t main_screen_index) { m_screen_rect = rects[main_screen_index]; }
+    void set_screen_rects(Vector<Web::DevicePixelRect> const& rects, size_t main_screen_index)
+    {
+        m_all_screen_rects = rects;
+        m_main_screen_index = main_screen_index;
+    }
     void set_device_pixel_ratio(double device_pixel_ratio) { m_device_pixel_ratio = device_pixel_ratio; }
     void set_zoom_level(double zoom_level) { m_zoom_level = zoom_level; }
     void set_maximum_frames_per_second(u64 maximum_frames_per_second);
@@ -110,7 +114,8 @@ private:
     virtual bool is_url_suitable_for_same_process_navigation(URL::URL const& current_url, URL::URL const& target_url) const override;
     virtual void request_new_process_for_navigation(URL::URL const&) override;
     virtual Gfx::Palette palette() const override;
-    virtual Web::DevicePixelRect screen_rect() const override { return m_screen_rect; }
+    virtual Web::DevicePixelRect screen_rect() const override { return m_all_screen_rects[m_main_screen_index]; }
+    virtual size_t screen_count() const override { return m_all_screen_rects.size(); }
     virtual Web::CSS::PreferredColorScheme preferred_color_scheme() const override { return m_preferred_color_scheme; }
     virtual Web::CSS::PreferredContrast preferred_contrast() const override { return m_preferred_contrast; }
     virtual Web::CSS::PreferredMotion preferred_motion() const override { return m_preferred_motion; }
@@ -194,7 +199,8 @@ private:
     PageHost& m_owner;
     GC::Ref<Web::Page> m_page;
     RefPtr<Gfx::PaletteImpl> m_palette_impl;
-    Web::DevicePixelRect m_screen_rect;
+    Vector<Web::DevicePixelRect> m_all_screen_rects { Web::DevicePixelRect {} };
+    size_t m_main_screen_index { 0 };
     double m_device_pixel_ratio { 1.0 };
     double m_zoom_level { 1.0 };
     double m_maximum_frames_per_second { 60.0 };

Services/WebWorker/PageHost.h

@@ -34,6 +34,7 @@ public:
     virtual Web::CSS::PreferredColorScheme preferred_color_scheme() const override;
     virtual Web::CSS::PreferredContrast preferred_contrast() const override;
     virtual Web::CSS::PreferredMotion preferred_motion() const override;
+    virtual size_t screen_count() const override { return 1; }
     virtual String page_did_request_cookie(URL::URL const&, Web::Cookie::Source) override;
     virtual void request_file(Web::FileRequest) override;
     virtual Web::DisplayListPlayerType display_list_player_type() const override { VERIFY_NOT_REACHED(); }

Tests/LibWeb/Text/expected/screen-is-extended.txt

@@ -0,0 +1,3 @@
+typeof screen.isExtended: boolean
+screen.isExtended: false
+

Tests/LibWeb/Text/input/screen-is-extended.html

@@ -0,0 +1,9 @@
+<!DOCTYPE html>
+<script src="include.js"></script>
+<script>
+    test(() => {
+        println(`typeof screen.isExtended: ${typeof screen.isExtended}`);
+        println(`screen.isExtended: ${screen.isExtended}`);
+    });
+</script>
+