Delete more probably unused plugin code.

third_party/WebKit/Source/web/WebPluginContainerImpl.h

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2014 Opera Software ASA. 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.
@@ skipping 71 matching lines @@
     // Widget methods
     void setFrameRect(const IntRect&) override;
     void paint(GraphicsContext&, const CullRect&) const override;
     void invalidateRect(const IntRect&) override;
     void setFocus(bool, WebFocusType) override;
     void show() override;
     void hide() override;
     void handleEvent(Event*) override;
     void frameRectsChanged() override;
     void setParentVisible(bool) override;
-    void setParent(Widget*) override;
     void widgetGeometryMayHaveChanged() override;
     bool isPluginContainer() const override { return true; }
     void eventListenersRemoved() override;
 
     // WebPluginContainer methods
     WebElement element() override;
     WebDocument document() override;
     void dispatchProgressEvent(const WebString& type, bool lengthComputable, unsigned long long loaded, unsigned long long total, const WebString& url) override;
     void enqueueMessageEvent(const WebDOMMessageEvent&) override;
     void invalidate() override;
@@ skipping 106 matching lines @@
 };
 
 DEFINE_TYPE_CASTS(WebPluginContainerImpl, Widget, widget, widget->isPluginContainer(), widget.isPluginContainer());
 // Unlike Widget, we need not worry about object type for container.
 // WebPluginContainerImpl is the only subclass of WebPluginContainer.
 DEFINE_TYPE_CASTS(WebPluginContainerImpl, WebPluginContainer, container, true, true);
 
 } // namespace blink
 
 #endif