Fix crash with print preview and the new scrollbar code that triggered an assert in WebKit side. ...

webkit/plugins/ppapi/ppb_scrollbar_impl.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef WEBKIT_PLUGINS_PPAPI_PPB_SCROLLBAR_IMPL_H_
 #define WEBKIT_PLUGINS_PPAPI_PPB_SCROLLBAR_IMPL_H_
 
 #include <vector>
 
+#include "base/task.h"
 #include "ppapi/thunk/ppb_scrollbar_api.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebRect.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebScrollbarClient.h"
 #include "ui/gfx/rect.h"
 #include "webkit/plugins/ppapi/ppb_widget_impl.h"
 
 namespace webkit {
 namespace ppapi {
 
 class PluginInstance;
@@ skipping 49 matching lines @@
   virtual void getTickmarks(
       WebKit::WebScrollbar* scrollbar,
       WebKit::WebVector<WebKit::WebRect>* tick_marks) const OVERRIDE;
 
   void NotifyInvalidate();
 
   gfx::Rect dirty_;
   std::vector<WebKit::WebRect> tickmarks_;
   scoped_ptr<WebKit::WebScrollbar> scrollbar_;
 
+  // Used so that the post task for Invalidate doesn't keep an extra reference.
+  ScopedRunnableMethodFactory<PPB_Scrollbar_Impl> method_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(PPB_Scrollbar_Impl);
 };
 
 }  // namespace ppapi
 }  // namespace webkit
 
 #endif  // WEBKIT_PLUGINS_PPAPI_PPB_SCROLLBAR_IMPL_H_