Move shelf item tooltip flag from delegate to item.

ash/shell/window_watcher_shelf_item_delegate.cc

Index: ash/shell/window_watcher_shelf_item_delegate.cc
diff --git a/ash/shell/window_watcher_shelf_item_delegate.cc b/ash/shell/window_watcher_shelf_item_delegate.cc
index 877037b3ce2b0e2e83306bc0a52a85a5df642b0d..9ac9c15bfa743ab7acbbc02183ff1cbf2453adb5 100644
--- a/ash/shell/window_watcher_shelf_item_delegate.cc
+++ b/ash/shell/window_watcher_shelf_item_delegate.cc
@@ -48,10 +48,6 @@ bool WindowWatcherShelfItemDelegate::CanPin() const {
   return true;
 }
 
-bool WindowWatcherShelfItemDelegate::ShouldShowTooltip() {
-  return true;
-}
-
 void WindowWatcherShelfItemDelegate::Close() {}
 
 }  // namespace shell