Fix memory leak of PreviewModeClient in PDF

pdf/out_of_process_instance.h

Index: pdf/out_of_process_instance.h
diff --git a/pdf/out_of_process_instance.h b/pdf/out_of_process_instance.h
index 1215f192bcf34c8c94220a8bcf9944676bcd8842..e7631344bad6e11b4b6edd4b4c910fac3c36eca1 100644
--- a/pdf/out_of_process_instance.h
+++ b/pdf/out_of_process_instance.h
@@ -257,6 +257,10 @@ class OutOfProcessInstance : public pp::Instance,
 
   scoped_ptr<PDFEngine> engine_;
 
+  // The PreviewModeClient used for print preview. Will be passed to
+  // |preview_engine_|.
+  scoped_ptr<PreviewModeClient> preview_client_;
+
   // This engine is used to render the individual preview page data. This is
   // used only in print preview mode. This will use |PreviewModeClient|
   // interface which has very limited access to the pp::Instance.