views: provide feedback when editing fails

ui/views/style/platform_style.h

Index: ui/views/style/platform_style.h
diff --git a/ui/views/style/platform_style.h b/ui/views/style/platform_style.h
index a4a33a1a6e41016fa85a33c4b630c0f8c3273e11..bc9eab35332e1e8bba1cdbbb0fb294d051be8170 100644
--- a/ui/views/style/platform_style.h
+++ b/ui/views/style/platform_style.h
@@ -92,6 +92,10 @@ class VIEWS_EXPORT PlatformStyle {
   static std::unique_ptr<Border> CreateThemedLabelButtonBorder(
       LabelButton* button);
 
+  // Called whenever a textfield keypress is unhandled for any reason. Gives
+  // visual/audio feedback about the unhandled key if platform-appropriate.
+  static void OnTextfieldKeypressUnhandled();
+
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PlatformStyle);
 };