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

webkit/plugins/ppapi/ppb_scrollbar_impl.h

Index: webkit/plugins/ppapi/ppb_scrollbar_impl.h
===================================================================
--- webkit/plugins/ppapi/ppb_scrollbar_impl.h	(revision 96306)
+++ webkit/plugins/ppapi/ppb_scrollbar_impl.h	(working copy)
@@ -7,6 +7,7 @@
 
 #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"
@@ -76,6 +77,9 @@
   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);
 };