Remove non-MD code from ShelfButton

ash/common/shelf/shelf_button.h

Index: ash/common/shelf/shelf_button.h
diff --git a/ash/common/shelf/shelf_button.h b/ash/common/shelf/shelf_button.h
index d52ef98fbf7ebe55a8af8e0c42651676c7abb06d..8e2bc3d4910ffb7958642bc00bce02cafeba6a38 100644
--- a/ash/common/shelf/shelf_button.h
+++ b/ash/common/shelf/shelf_button.h
@@ -9,7 +9,10 @@
 #include "base/macros.h"
 #include "ui/gfx/shadow_value.h"
 #include "ui/views/controls/button/custom_button.h"
-#include "ui/views/controls/image_view.h"
+
+namespace views {
+class ImageView;
+}
 
 namespace ash {
 class InkDropButtonListener;