Handle long press in PDF documents.

pdf/preview_mode_client.h

Index: pdf/preview_mode_client.h
diff --git a/pdf/preview_mode_client.h b/pdf/preview_mode_client.h
index 676d71891612172464fd73f3bf3ac71064db3464..82c0792b027da9904d08dcbe76db44ff0f1b9619 100644
--- a/pdf/preview_mode_client.h
+++ b/pdf/preview_mode_client.h
@@ -58,6 +58,7 @@ class PreviewModeClient : public PDFEngine::Client {
   std::string ShowFileSelectionDialog() override;
   pp::URLLoader CreateURLLoader() override;
   void ScheduleCallback(int id, int delay_in_ms) override;
+  void ScheduleTouchTimerCallback(int id, int delay_in_ms) override;
   void SearchString(const base::char16* string,
                     const base::char16* term,
                     bool case_sensitive,