Use a depfile to know when to regenerate notice files

android_webview/BUILD.gn

 # Copyright 2015 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("//android_webview/system_webview_apk_tmpl.gni")
 import("//android_webview/webview_repack_locales.gni")
 import("//build/config/android/config.gni")
 import("//build/config/android/rules.gni")
 import("//build/config/locales.gni")
 import("//components/spellcheck/spellcheck_build_features.gni")
@@ skipping 131 matching lines @@
 android_assets("assets") {
   deps = [
     ":locale_pak_assets",
     ":monochrome_webview_assets",
     ":pak_file_assets",
   ]
 }
 
 action("generate_webview_license_notice") {
   script = "tools/webview_licenses.py"
-  inputs = exec_script("//android_webview/tools/webview_licenses.py",
-                       [ "gn_notice_deps" ],
-                       "value")
-  inputs += [ "tools/licenses_notice.tmpl" ]
+  depfile = "$target_gen_dir/$target_name.d"
+  inputs = [
+    "tools/licenses_notice.tmpl",
+  ]
   outputs = [
     webview_license_path,
   ]
   args = [
     "notice",
-    rebase_path(webview_license_path),
+    rebase_path(webview_license_path, root_build_dir),
+    "--depfile",
+    rebase_path(depfile, root_build_dir),
   ]
 }
 
 android_resources("system_webview_resources") {
   resource_dirs = [ "apk/java/res" ]
   custom_package = system_webview_package_name
 }
 
 android_resources("resources") {
   resource_dirs = [ "java/res" ]
@@ skipping 613 matching lines @@
   system_webview_apk_tmpl("system_webview_apk") {
     android_manifest = system_webview_android_manifest
     android_manifest_dep = ":system_webview_manifest"
     deps = [
       ":system_webview_resources",
       "//android_webview/glue",
     ]
     apk_name = "SystemWebView"
   }
 }