Use a depfile to know when to regenerate notice files

remoting/webapp/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.
 
 # Keep in sync with targets in remoting/remoting_client.gypi.
 
 import("//build/config/features.gni")
 import("//remoting/webapp/build_template.gni")
 import("//remoting/webapp/files.gni")
 
 action("credits") {
   about_credits_file = "$target_gen_dir/credits.html"
   script = "//tools/licenses.py"
+  depfile = "$target_gen_dir/$target_name.d"
 
   inputs = [
     "base/html/credits.tmpl",
     "base/html/credits_entry.tmpl",
   ]
 
   outputs = [
     about_credits_file,
   ]
 
   args = [
     "credits",
     rebase_path(about_credits_file, root_build_dir),
     "--file-template",
     rebase_path("base/html/credits.tmpl", root_build_dir),
     "--entry-template",
     rebase_path("base/html/credits_entry.tmpl", root_build_dir),
+    "--depfile",
+    rebase_path(depfile, root_build_dir),
   ]
 }
 
 desktop_remoting_webapp("webapp") {
   output_dir = "$root_build_dir/remoting/remoting-webapp.v2"
   zip_path = "$root_build_dir/remoting-webapp.v2.zip"
   extra_files = [ "crd/remoting_client_pnacl.nmf.jinja2" ]
 }
 
 copy("browser_test_resources") {
@@ skipping 54 matching lines @@
 }
 
 build_webapp_html("unittest_html") {
   html_template_file = remoting_webapp_unittests_template_main
   html_template_include_files = []
   js_files = remoting_webapp_unittests_all_js_files
   html_output = "$remoting_unit_test_out_dir/unittests.html"
   exclude_js = remoting_webapp_unittests_exclude_js_files
   instrument_js = webapp_js_files
 }