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

third_party/WebKit/Source/web/FrameLoaderClientImpl.h

 /*
  * Copyright (C) 2009, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2011 Apple 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.
@@ skipping 23 matching lines @@
 
 #include "core/loader/FrameLoaderClient.h"
 #include "platform/heap/Handle.h"
 #include "platform/weborigin/KURL.h"
 #include "wtf/PassOwnPtr.h"
 #include "wtf/RefPtr.h"
 
 namespace blink {
 
 class WebLocalFrameImpl;
-class WebPluginLoadObserver;
 
 class FrameLoaderClientImpl final : public FrameLoaderClient {
 public:
     static PassOwnPtrWillBeRawPtr<FrameLoaderClientImpl> create(WebLocalFrameImpl*);
 
     ~FrameLoaderClientImpl() override;
 
     DECLARE_VIRTUAL_TRACE();
 
     WebLocalFrameImpl* webFrame() const { return m_webFrame.get(); }
@@ skipping 120 matching lines @@
 
     unsigned backForwardLength() override;
 
     void suddenTerminationDisablerChanged(bool present, SuddenTerminationDisablerType) override;
 
 private:
     explicit FrameLoaderClientImpl(WebLocalFrameImpl*);
 
     bool isFrameLoaderClientImpl() const override { return true; }
 
-    PassOwnPtrWillBeRawPtr<WebPluginLoadObserver> pluginLoadObserver(DocumentLoader*);
-
     // The WebFrame that owns this object and manages its lifetime. Therefore,
     // the web frame object is guaranteed to exist.
     RawPtrWillBeMember<WebLocalFrameImpl> m_webFrame;
 };
 
 DEFINE_TYPE_CASTS(FrameLoaderClientImpl, FrameLoaderClient, client, client->isFrameLoaderClientImpl(), client.isFrameLoaderClientImpl());
 
 } // namespace blink
 
 #endif