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

third_party/WebKit/Source/core/html/PluginDocument.cpp

 /*
  * Copyright (C) 2006, 2008 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 117 matching lines @@
         createDocumentStructure();
 
     if (!length)
         return;
     if (PluginView* view = pluginView())
         view->didReceiveData(data, length);
 }
 
 void PluginDocumentParser::finish()
 {
-    if (PluginView* view = pluginView()) {
-        const ResourceError& error = document()->loader()->mainDocumentError();
-        if (error.isNull())
-            view->didFinishLoading();
-        else
-            view->didFailLoading(error);
-        m_embedElement = nullptr;
-    }
+    m_embedElement = nullptr;
     RawDataDocumentParser::finish();
 }
 
 PluginView* PluginDocumentParser::pluginView() const
 {
     if (Widget* widget = toPluginDocument(document())->pluginWidget()) {
         ASSERT_WITH_SECURITY_IMPLICATION(widget->isPluginContainer());
         return toPluginView(widget);
     }
     return 0;
@@ skipping 32 matching lines @@
     HTMLDocument::detach(context);
 }
 
 DEFINE_TRACE(PluginDocument)
 {
     visitor->trace(m_pluginNode);
     HTMLDocument::trace(visitor);
 }
 
 }