Add Hide and Show to the app list SearchBoxView.

ui/app_list/views/search_box_view_delegate.h

Index: ui/app_list/views/search_box_view_delegate.h
diff --git a/ui/app_list/views/search_box_view_delegate.h b/ui/app_list/views/search_box_view_delegate.h
index cdbf23878bb7157ad1b73ef6291b2cae29b4e9de..59a4e3075a81aaf9723594484228997afed319a0 100644
--- a/ui/app_list/views/search_box_view_delegate.h
+++ b/ui/app_list/views/search_box_view_delegate.h
@@ -16,6 +16,9 @@ class APP_LIST_EXPORT SearchBoxViewDelegate {
   // Invoked when query text has changed by the user.
   virtual void QueryChanged(SearchBoxView* sender) = 0;
 
+  // Invoked when the view's visibility has been altered.
+  virtual void SearchBoxVisibilityChanged(SearchBoxView* sender) = 0;
+
  protected:
   virtual ~SearchBoxViewDelegate() {}
 };