Add "Show saved copy" button in dino page when there's offline copy

components/error_page/common/net_error_info.h

Index: components/error_page/common/net_error_info.h
diff --git a/components/error_page/common/net_error_info.h b/components/error_page/common/net_error_info.h
index 1f637e5235ac33329316b211746a108504f7f397..42f528b7e5eddd20fad0b0c8f9fc9bc805dfdd8c 100644
--- a/components/error_page/common/net_error_info.h
+++ b/components/error_page/common/net_error_info.h
@@ -41,10 +41,13 @@ enum NetworkErrorPageEvent {
 
   NETWORK_ERROR_DIAGNOSE_BUTTON_CLICKED = 17,      // Diagnose button clicked.
 
-  // For the "Show all saved pages".
-  NETWORK_ERROR_PAGE_SHOW_SAVED_PAGES_BUTTON_SHOWN = 18,
-  NETWORK_ERROR_PAGE_SHOW_SAVED_PAGES_BUTTON_CLICKED = 19,
-  NETWORK_ERROR_PAGE_SHOW_SAVED_PAGES_BUTTON_ERROR = 20,
+  // For the button to show all offline pages.
+  NETWORK_ERROR_PAGE_SHOW_OFFLINE_PAGES_BUTTON_SHOWN = 18,
+  NETWORK_ERROR_PAGE_SHOW_OFFLINE_PAGES_BUTTON_CLICKED = 19,
+
+  // For the button to show offline copy.
+  NETWORK_ERROR_PAGE_SHOW_OFFLINE_COPY_BUTTON_SHOWN = 20,
+  NETWORK_ERROR_PAGE_SHOW_OFFLINE_COPY_BUTTON_CLICKED = 21,
 
   NETWORK_ERROR_PAGE_EVENT_MAX,
 };