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

third_party/WebKit/Source/core/loader/DocumentLoader.cpp

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc. All rights reserved.
  * 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:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 199 matching lines @@
 }
 
 void DocumentLoader::mainReceivedError(const ResourceError& error)
 {
     ASSERT(!error.isNull());
     ASSERT(!mainResourceLoader() || !mainResourceLoader()->defersLoading() || InspectorInstrumentation::isDebuggerPaused(m_frame));
     if (m_applicationCacheHost)
         m_applicationCacheHost->failedLoadingMainResource();
     if (!frameLoader())
         return;
-    m_mainDocumentError = error;
     if (m_state < MainResourceDone)
         m_state = MainResourceDone;
     frameLoader()->receivedMainResourceError(this, error);
     clearMainResourceHandle();
 }
 
 // Cancels the data source's pending loads.  Conceptually, a data source only loads
 // one document at a time, but one document may have many related resources.
 // stopLoading will stop all loads initiated by the data source,
 // but not loads initiated by child frames' data sources -- that's the WebFrame's job.
@@ skipping 485 matching lines @@
     if (m_request.url().isEmpty() && !frameLoader()->stateMachine()->creatingInitialEmptyDocument())
         m_request.setURL(blankURL());
     m_response = ResourceResponse(m_request.url(), "text/html", 0, nullAtom, String());
     finishedLoading(monotonicallyIncreasingTime());
     return true;
 }
 
 void DocumentLoader::startLoadingMainResource()
 {
     RefPtrWillBeRawPtr<DocumentLoader> protect(this);
-    m_mainDocumentError = ResourceError();
     timing().markNavigationStart();
     ASSERT(!m_mainResource);
     ASSERT(m_state == NotStarted);
     m_state = Provisional;
 
     if (maybeLoadEmpty())
         return;
 
     ASSERT(timing().navigationStart());
     ASSERT(!timing().fetchStart());
@@ skipping 97 matching lines @@
 {
     m_writer = createWriterFor(ownerDocument, init, mimeType(), m_writer ? m_writer->encoding() : emptyAtom, true, ForceSynchronousParsing);
     if (!source.isNull())
         m_writer->appendReplacingData(source);
     endWriting(m_writer.get());
 }
 
 DEFINE_WEAK_IDENTIFIER_MAP(DocumentLoader);
 
 } // namespace blink