Use a check item instead of changing its text.

chrome/browser/tab_contents/render_view_context_menu.cc

Index: chrome/browser/tab_contents/render_view_context_menu.cc
===================================================================
--- chrome/browser/tab_contents/render_view_context_menu.cc	(revision 124915)
+++ chrome/browser/tab_contents/render_view_context_menu.cc	(working copy)
@@ -679,6 +679,11 @@
   menu_model_.AddItem(command_id, title);
 }
 
+void RenderViewContextMenu::AddCheckItem(int command_id,
+                                         const string16& title) {
+  menu_model_.AddCheckItem(command_id, title);
+}
+
 void RenderViewContextMenu::AddSeparator() {
   menu_model_.AddSeparator();
 }