Require the cursor to move a minimum distance after the mouse press before initiating a mouse drag

ash/shelf/shelf_view.h

Index: ash/shelf/shelf_view.h
diff --git a/ash/shelf/shelf_view.h b/ash/shelf/shelf_view.h
index c3fb39f923ed6b503281ddca7a44fb8ae89ed5ec..f68e959945704915d41b1e538bb7e45da0da0cfb 100644
--- a/ash/shelf/shelf_view.h
+++ b/ash/shelf/shelf_view.h
@@ -358,8 +358,8 @@ class ASH_EXPORT ShelfView : public views::View,
   // |dragging_| is set only if the mouse is dragged far enough.
   views::View* drag_view_;
 
-  // X coordinate of the mouse down event in |drag_view_|s coordinates.
-  int drag_offset_;
+  // Position of the mouse down event in |drag_view_|'s coordinates.
+  gfx::Point drag_origin_;
 
   // Index |drag_view_| was initially at.
   int start_drag_index_;