LibWeb: Implement Window.prompt()

Author: https://github.com/linusg
Commit: 5e07c27e25
Pull-request: https://github.com/SerenityOS/serenity/pull/5423
Reviewed-by: https://github.com/awesomekling

Userland/Libraries/LibWeb/OutOfProcessWebView.cpp

@@ -28,6 +28,7 @@
 #include "WebContentClient.h"
 #include <AK/String.h>
 #include <AK/URLParser.h>
+#include <LibGUI/InputBox.h>
 #include <LibGUI/MessageBox.h>
 #include <LibGUI/Painter.h>
 #include <LibGUI/ScrollBar.h>
@@ -293,6 +294,14 @@ bool OutOfProcessWebView::notify_server_did_request_confirm(Badge<WebContentClie
     return confirm_result == GUI::Dialog::ExecResult::ExecOK;
 }
 
+String OutOfProcessWebView::notify_server_did_request_prompt(Badge<WebContentClient>, const String& message, const String& default_)
+{
+    String response { default_ };
+    if (GUI::InputBox::show(window(), response, message, "Prompt") == GUI::InputBox::ExecOK)
+        return response;
+    return {};
+}
+
 void OutOfProcessWebView::did_scroll()
 {
     client().post_message(Messages::WebContentServer::SetViewportRect(visible_content_rect()));