Replace IDR window property use with gfx::ImageSkia icons.

ash/common/shelf/shelf_constants.h

Index: ash/common/shelf/shelf_constants.h
diff --git a/ash/common/shelf/shelf_constants.h b/ash/common/shelf/shelf_constants.h
index bd80e6b66a6c5dad863fedb3ab428432ab6ccce9..708e2adbe3b1601d128443a1a6ef841bbfe2890b 100644
--- a/ash/common/shelf/shelf_constants.h
+++ b/ash/common/shelf/shelf_constants.h
@@ -28,9 +28,6 @@ enum ShelfConstant {
   SHELF_INSETS_FOR_AUTO_HIDE
 };
 
-// Invalid image resource id used for shelf items.
-const int kInvalidImageResourceID = -1;
-
 // We reserve a small area on the edge of the workspace area to ensure that
 // the resize handle at the edge of the window can be hit.
 extern const int kWorkspaceAreaVisibleInset;