LibWeb: Helper for creating load requests with a Cookie header

Instead of all interested parties needing to write out the code to get
the cookie value for a load request, add a static helper to do it in
one location.

Userland/Libraries/LibWeb/CMakeLists.txt

@@ -193,6 +193,7 @@ set(SOURCES
     Loader/FrameLoader.cpp
     Loader/ImageLoader.cpp
     Loader/ImageResource.cpp
+    Loader/LoadRequest.cpp
     Loader/Resource.cpp
     Loader/ResourceLoader.cpp
     Namespace.cpp