Split app list drop target into reorder and folder drop targets.

ui/app_list/views/apps_grid_view.h

Index: ui/app_list/views/apps_grid_view.h
diff --git a/ui/app_list/views/apps_grid_view.h b/ui/app_list/views/apps_grid_view.h
index f509284b54e61b51c504acf79ee89fda1b968f8c..f10758a19a3d00b9d77d893c86129dac714b9dfe 100644
--- a/ui/app_list/views/apps_grid_view.h
+++ b/ui/app_list/views/apps_grid_view.h
@@ -390,9 +390,9 @@ class APP_LIST_EXPORT AppsGridView : public views::View,
   // dropped into it.
   bool CanDropIntoTarget(const Index& drop_target);
 
-  // Returns the visual index of the nearest tile in which |drag_view_| enters
-  // either its re-ordering or folder dropping circle.
-  Index GetNearestTileForDragView();
+  // Calculates the visual index of the nearest tile for which |drag_view_|
+  // enters either its re-ordering or folder dropping circle.
+  void CalculateNearestTileForDragView();
 
   // Calculates |nearest_tile| in which |vertex| of the |drag_view| is
   // enclosed.
@@ -513,7 +513,14 @@ class APP_LIST_EXPORT AppsGridView : public views::View,
 #endif
 
   Pointer drag_pointer_;
-  Index drop_target_;
+
+  // The most recent reorder drop target.
+  Index reorder_drop_target_;
+
+  // The most recent folder drop target.
+  Index folder_drop_target_;
+
+  // The current action that ending a drag will perform.
   DropAttempt drop_attempt_;
 
   // Timer for re-ordering the |drop_target_| and |drag_view_|.