Add "previewing on hover" support for password field.

components/autofill/content/renderer/autofill_agent.h

Index: components/autofill/content/renderer/autofill_agent.h
diff --git a/components/autofill/content/renderer/autofill_agent.h b/components/autofill/content/renderer/autofill_agent.h
index deca2359cff08760ee30ae41b0b059d3ee356e2a..daa19e9b2163628ce10ce8b568deb21c9fb4ca99 100644
--- a/components/autofill/content/renderer/autofill_agent.h
+++ b/components/autofill/content/renderer/autofill_agent.h
@@ -105,6 +105,8 @@ class AutofillAgent : public content::RenderViewObserver,
   void OnAcceptDataListSuggestion(const base::string16& value);
   void OnAcceptPasswordAutofillSuggestion(const base::string16& username,
                                           const base::string16& password);
+  void OnPreviewPasswordAutofillSuggestion(const base::string16& username,
+                                           const base::string16& password);
 
   // Called when interactive autocomplete finishes. |message| is printed to
   // the console if non-empty.