(Merge to M-51) Revise the shelf alignment locking mechanism.

ash/shelf/shelf_util.h

Index: ash/shelf/shelf_util.h
diff --git a/ash/shelf/shelf_util.h b/ash/shelf/shelf_util.h
index 799e59f082c3dcdd9919d201b7e4820b8500118a..65b893d8fa442616627ade0c62ae576cb2cd4e1b 100644
--- a/ash/shelf/shelf_util.h
+++ b/ash/shelf/shelf_util.h
@@ -7,6 +7,7 @@
 
 #include "ash/ash_export.h"
 #include "ash/shelf/shelf_item_types.h"
+#include "ash/shelf/shelf_types.h"
 #include "base/strings/string16.h"
 #include "ui/aura/window.h"
 
@@ -54,6 +55,9 @@ ASH_EXPORT void ClearShelfItemDetailsForWindow(aura::Window* window);
 ASH_EXPORT const ShelfItemDetails* GetShelfItemDetailsForWindow(
     aura::Window* window);
 
+// Returns true if the shelf |alignment| is horizontal.
+ASH_EXPORT bool IsHorizontalAlignment(ShelfAlignment alignment);
+
 }  // namespace ash
 
 #endif  // ASH_SHELF_SHELF_UTIL_H_