Adds test coverage for 521663

Source/web/tests/FrameTestHelpers.h

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 144 matching lines @@
         EXPECT_TRUE(ScrollbarTheme::theme()->usesOverlayScrollbars());
     }
 
     ~UseMockScrollbarSettings()
     {
         Settings::setMockScrollbarsEnabled(false);
         RuntimeEnabledFeatures::setOverlayScrollbarsEnabled(false);
     }
 };
 
+// Task that calls loadRequest() when run().
+class LoadTask : public WebThread::Task {
+public:
+    LoadTask(WebFrame*, const WebURLRequest&);
+
+    void run() override;
+
+private:
+    WebFrame* const m_frame;
+    const WebURLRequest m_request;
+};
+
 } // namespace FrameTestHelpers
 } // namespace blink
 
 #endif // FrameTestHelpers_h