Update onbeforeunload cancel string.

components/app_modal_strings.grdp

 <?xml version="1.0" encoding="utf-8"?>
 <grit-part>
 
   <!-- JavaScript Dialog Box strings -->
   <message name="IDS_JAVASCRIPT_MESSAGEBOX_TITLE" desc="Title for JavaScript prompt and confirm originating from a webpage">
     <ph name="SITE">$1<ex>http://www.google.com</ex></ph> says:
   </message>
   <message name="IDS_JAVASCRIPT_MESSAGEBOX_TITLE_IFRAME" desc="Title for JavaScript prompt and confirm originating from an iframe inside the webpage">
     An embedded page at <ph name="SITE">$1<ex>http://www.google.com</ex></ph> says:
   </message>
@@ skipping 11 matching lines @@
   <message name="IDS_BEFOREUNLOAD_MESSAGEBOX_TITLE" desc="Title for the 'before unload' dialog.">
     Do you want to leave this site?
   </message>
   <message name="IDS_BEFOREUNLOAD_MESSAGEBOX_MESSAGE" desc="Text shown as the message of the 'before unload' dialog.">
     Changes you made may not be saved.
   </message>
   <message name="IDS_BEFOREUNLOAD_MESSAGEBOX_OK_BUTTON_LABEL" desc="The text on the button which navigates the user away from the page.">
     Leave
   </message>
   <message name="IDS_BEFOREUNLOAD_MESSAGEBOX_CANCEL_BUTTON_LABEL" desc="The text on the button which cancels the navigation away from the page.">
-    Stay
+    Remain
   </message>
 
   <!-- "Before Reload" Dialog Box strings (same as "Before Unload" but when reloading rather than unloading the page -->
   <message name="IDS_BEFORERELOAD_MESSAGEBOX_TITLE" desc="Title for the 'before unload' dialog for reloads.">
     Do you want to reload this site?
   </message>
   <message name="IDS_BEFORERELOAD_MESSAGEBOX_OK_BUTTON_LABEL" desc="The text on the button which reloads the page.">
     Reload
   </message>
   <message name="IDS_BEFORERELOAD_MESSAGEBOX_CANCEL_BUTTON_LABEL" desc="The text on the button which cancels the page reload.">
     Don’t Reload
   </message>
 
 </grit-part>