Pass shelf instances, not root windows, for ash context menus.

ash/shelf/shelf.h

Index: ash/shelf/shelf.h
diff --git a/ash/shelf/shelf.h b/ash/shelf/shelf.h
index 597dd37aca3b6c846b8e659fef2f021a1376944d..f8844586a7a6ad57df53539942186cf705abcfbd 100644
--- a/ash/shelf/shelf.h
+++ b/ash/shelf/shelf.h
@@ -60,6 +60,10 @@ class ASH_EXPORT Shelf {
   ShelfAlignment alignment() const { return alignment_; }
   bool IsHorizontalAlignment() const;
 
+  // Sets the ShelfAutoHideBehavior. See enum description for details.
+  void SetAutoHideBehavior(ShelfAutoHideBehavior behavior);
+  ShelfAutoHideBehavior GetAutoHideBehavior() const;
+
   // A helper functions that chooses values specific to a shelf alignment.
   template <typename T>
   T SelectValueForShelfAlignment(T bottom, T left, T right, T top) const {