Add note to ui/gfx/vector_icons/BUILD to reduce developer confusion as

ui/gfx/vector_icons/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/chrome_build.gni")
 
+# NB: This is a deprecated vector icon target that should be removed. Add vector
+# icons to a more specific target, or ui/vector_icons if ui/ is the right place
+# for them. TODO(estade): remove this target.
 action("aggregate_vector_icons") {
   visibility = [ ":*" ]
 
   script = "aggregate_vector_icons.py"
 
   icons = [
     "account_box.icon",
     "account_child.icon",
     "account_child_circle.icon",
     "account_circle.icon",
@@ skipping 77 matching lines @@
     "../vector_icon_types.h",
     "../vector_icons_public.h",
   ]
 
   deps = [
     ":aggregate_vector_icons",
     "//base",
     "//skia",
   ]
 }