LibWeb: Let HTML::EventLoop drive the firing of resize events

Userland/Libraries/LibWeb/DOM/Document.cpp

@@ -57,6 +57,7 @@
 #include <LibWeb/Page/BrowsingContext.h>
 #include <LibWeb/Page/Page.h>
 #include <LibWeb/SVG/TagNames.h>
+#include <LibWeb/UIEvents/EventNames.h>
 #include <LibWeb/UIEvents/KeyboardEvent.h>
 #include <LibWeb/UIEvents/MouseEvent.h>
 
@@ -1083,4 +1084,25 @@ String Document::visibility_state() const
     return hidden() ? "hidden" : "visible";
 }
 
+// https://drafts.csswg.org/cssom-view/#run-the-resize-steps
+void Document::run_the_resize_steps()
+{
+    // 1. If doc’s viewport has had its width or height changed
+    //    (e.g. as a result of the user resizing the browser window, or changing the page zoom scale factor,
+    //    or an iframe element’s dimensions are changed) since the last time these steps were run,
+    //    fire an event named resize at the Window object associated with doc.
+
+    if (!browsing_context())
+        return;
+
+    auto viewport_size = browsing_context()->viewport_rect().size();
+    if (m_last_viewport_size == viewport_size)
+        return;
+    m_last_viewport_size = viewport_size;
+
+    dispatch_event(DOM::Event::create(UIEvents::EventNames::resize));
+
+    update_layout();
+}
+
 }

Userland/Libraries/LibWeb/DOM/Document.h

@@ -301,6 +301,8 @@ public:
     bool hidden() const;
     String visibility_state() const;
 
+    void run_the_resize_steps();
+
 private:
     explicit Document(const AK::URL&);
 
@@ -388,6 +390,9 @@ private:
 
     // https://html.spec.whatwg.org/#page-showing
     bool m_page_showing { false };
+
+    // Used by run_the_resize_steps().
+    Gfx::IntSize m_last_viewport_size;
 };
 
 }