Improve print preview checks in the PDF plugin

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 e2c0eacfde32047075967512fa26b1ca9d860d0a..6b22f7a905fd402b1eb5669ca9c23919ba1daf8c 100644
--- a/pdf/out_of_process_instance.h
+++ b/pdf/out_of_process_instance.h
@@ -371,6 +371,9 @@ class OutOfProcessInstance : public pp::Instance,
     ACCESSIBILITY_STATE_LOADED
   } accessibility_state_;
 
+  // True if the plugin is loaded in print preview, otherwise false.
+  bool is_print_preview_;
+
   DISALLOW_COPY_AND_ASSIGN(OutOfProcessInstance);
 };