Remove PluginLoadObserver and related logic, it was only used for NPAPI.

third_party/WebKit/Source/web/tests/FakeWebPlugin.h

 /*
  * Copyright (C) 2012 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 46 matching lines @@
     void updateGeometry(const WebRect& clientRect, const WebRect& clipRect, const WebRect& windowClipRect, const WebVector<WebRect>& cutOutsRects, bool isVisible) override { }
     void updateFocus(bool, WebFocusType) override { }
     void updateVisibility(bool) override { }
     bool acceptsInputEvents() override { return true; }
     WebInputEventResult handleInputEvent(const WebInputEvent&, WebCursorInfo&) override { return WebInputEventResult::NotHandled; }
     bool handleDragStatusUpdate(WebDragStatus, const WebDragData&, WebDragOperationsMask, const WebPoint& position, const WebPoint& screenPosition) override { return false; }
     void didReceiveResponse(const WebURLResponse&) override { }
     void didReceiveData(const char* data, int dataLength) override { }
     void didFinishLoading() override { }
     void didFailLoading(const WebURLError&) override { }
-    void didFinishLoadingFrameRequest(const WebURL&, void* notifyData) override { }
-    void didFailLoadingFrameRequest(const WebURL&, void* notifyData, const WebURLError&) override { }
     bool isPlaceholder() override { return false; }
 
 protected:
     virtual ~FakeWebPlugin();
 
     WebPluginContainer* container() const { return m_container; }
 
 private:
     WebFrame* m_frame;
     WebPluginContainer* m_container;
 };
 
 } // namespace blink
 
 #endif // FakeWebPlugin_h