LibWeb: Set Cookie header on <img> and <object> resource requests

This required passing a reference to the owning HTML*Element to
ImageLoader, the same way that CSSLoader has a reference to its owner.

Userland/Libraries/LibWeb/Loader/ImageLoader.h

@@ -34,7 +34,7 @@ namespace Web {
 
 class ImageLoader : public ImageResourceClient {
 public:
-    ImageLoader();
+    ImageLoader(DOM::Element& owner_element);
 
     void load(const URL&);
 
@@ -69,6 +69,8 @@ private:
         Failed,
     };
 
+    DOM::Element& m_owner_element;
+
     mutable bool m_visible_in_viewport { false };
 
     size_t m_current_frame_index { 0 };