Make launching apps from shelf more intuitive

ash/shelf/wm_shelf.h

Index: ash/shelf/wm_shelf.h
diff --git a/ash/shelf/wm_shelf.h b/ash/shelf/wm_shelf.h
index 491f35e1b3ae4369371787afdf5671ffad546928..7ddee0d2fa1e89372ab6323d7b9f99c7ac1e5d2d 100644
--- a/ash/shelf/wm_shelf.h
+++ b/ash/shelf/wm_shelf.h
@@ -125,6 +125,10 @@ class ASH_EXPORT WmShelf : public ShelfLayoutManagerObserver {
   // Activates the shelf item specified by the index in the list of shelf items.
   static void ActivateShelfItem(int item_index);
 
+  // Activates the shelf item specified by the index in the list of shelf items
+  // on the display identified by |display_id|.
+  static void ActivateShelfItemOnDisplay(int item_index, int64_t display_id);
+
   // Handles a gesture |event| coming from a source outside the shelf widget
   // (e.g. the status area widget). Allows support for behaviors like toggling
   // auto-hide with a swipe, even if that gesture event hits another window.