Use a depfile to know when to regenerate notice files

remoting/host/installer/BUILD.gn

 # Copyright 2016 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("//remoting/build/config/remoting_build.gni")
 
 action("credits") {
   # We put this in $root_build_dir/gen/remoting instead of
   # $root_build_dir/gen/remoting/host (target_gen_dir) for
   # compatibility w/ GYP, since the installer needs the file to
   # be at the same location.
   about_credits_file = "$root_build_dir/gen/remoting/CREDITS.txt"
   script = "//tools/licenses.py"
+  depfile = "$target_gen_dir/$target_name.d"
 
   inputs = [
     "credits.tmpl",
     "credits_entry.tmpl",
   ]
 
   outputs = [
     about_credits_file,
   ]
 
   args = [
     "credits",
     rebase_path(about_credits_file, root_build_dir),
     "--file-template",
     rebase_path("credits.tmpl", root_build_dir),
     "--entry-template",
     rebase_path("credits_entry.tmpl", root_build_dir),
+    "--depfile",
+    rebase_path(depfile, root_build_dir),
   ]
 }