WebContent: Added IPC calls for getting source

Author: https://github.com/xeons
Commit: 306501fd4a
Pull-request: https://github.com/SerenityOS/serenity/pull/5477
Reviewed-by: https://github.com/awesomekling

Userland/Services/WebContent/WebContentClient.ipc

@@ -17,4 +17,5 @@ endpoint WebContentClient = 90
     DidRequestAlert(String message) => ()
     DidRequestConfirm(String message) => (bool result)
     DidRequestPrompt(String message, String default_) => (String response)
+    DidGetSource(URL url, String source) =|
 }