Implement Middle Click Autoscroll on all platforms not just Windows

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

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008 Alp Toker <alp@atoker.com>
  * Copyright (C) Research In Motion Limited 2009. All rights reserved.
  * Copyright (C) 2011 Kris Jordan <krisjordan@gmail.com>
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ skipping 745 matching lines @@
     // If we have a provisional request for a different document, a fragment scroll should cancel it.
     detachDocumentLoader(m_provisionalDocumentLoader);
     if (!m_frame->host())
         return;
     AutoReset<FrameLoadType> loadTypeChange(&m_loadType, frameLoadType);
     saveScrollState();
 
     KURL oldURL = m_frame->document()->url();
     bool hashChange = equalIgnoringFragmentIdentifier(url, oldURL) && url.fragmentIdentifier() != oldURL.fragmentIdentifier();
     if (hashChange) {
-        // If we were in the autoscroll/panScroll mode we want to stop it before following the link to the anchor
+        // If we were in the autoscroll/middleClickAutoscroll mode we want to stop it before following the link to the anchor
         m_frame->eventHandler().stopAutoscroll();
         m_frame->localDOMWindow()->enqueueHashchangeEvent(oldURL, url);
     }
     m_documentLoader->setIsClientRedirect(clientRedirect == ClientRedirectPolicy::ClientRedirect);
     updateForSameDocumentNavigation(url, SameDocumentNavigationDefault, nullptr, ScrollRestorationAuto, frameLoadType, initiatingDocument);
 
     m_documentLoader->initialScrollState().wasScrolledByUser = false;
 
     checkCompleted();
 
@@ skipping 838 matching lines @@
     tracedValue->setString("documentLoaderURL", m_documentLoader ? m_documentLoader->url() : String());
     return tracedValue;
 }
 
 inline void FrameLoader::takeObjectSnapshot() const
 {
     TRACE_EVENT_OBJECT_SNAPSHOT_WITH_ID("loading", "FrameLoader", this, toTracedValue());
 }
 
 } // namespace blink