Oilpan: Ensure that classes with virtual trace methods always have vtables for their left-most base…

Source/core/fetch/ResourceClient.h

 /*
     Copyright (C) 1998 Lars Knoll (knoll@mpi-hd.mpg.de)
     Copyright (C) 2001 Dirk Mueller <mueller@kde.org>
     Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
 
     This library is free software; you can redistribute it and/or
     modify it under the terms of the GNU Library General Public
     License as published by the Free Software Foundation; either
     version 2 of the License, or (at your option) any later version.
 
     This library is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     Library General Public License for more details.
 
     You should have received a copy of the GNU Library General Public License
     along with this library; see the file COPYING.LIB.  If not, write to
     the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
     Boston, MA 02110-1301, USA.
 
     This class provides all functionality needed for loading images, style sheets and html
     pages from the web. It has a memory cache for these objects.
 */
 
 #ifndef ResourceClient_h
 #define ResourceClient_h
 
+#include "platform/heap/Handle.h"

[Mads Ager (chromium), 2014/08/12 06:07:04]

You should be able to just forward declare Visitor (in the same way it is done
for Resource) instead of including Handle.h here.

[haraken, 2014/08/12 06:15:50]

I don't have a strong opinion here, but I guess that the current rule would be
just "include Handle.h so that the code compiles". Given that Handle.h has no
risk of creating include cycles, the rule will just work. (We're following the
rule for v8.h.)

 #include "wtf/FastAllocBase.h"
 #include "wtf/Forward.h"
 
 namespace blink {
 class Resource;
 
 class ResourceClient {
 public:
     enum ResourceClientType {
         BaseResourceType,
         ImageType,
         FontType,
         StyleSheetType,
         DocumentType,
         RawResourceType
     };
 
     virtual ~ResourceClient() { }
     virtual void notifyFinished(Resource*) { }
 
     static ResourceClientType expectedType() { return BaseResourceType; }
     virtual ResourceClientType resourceClientType() const { return expectedType(); }
 
+    virtual void trace(Visitor*) { }
+
 protected:
     ResourceClient() { }
 };
 }
 
 #endif