Use a depfile to know when to regenerate notice files

components/resources/BUILD.gn

Index: components/resources/BUILD.gn
diff --git a/components/resources/BUILD.gn b/components/resources/BUILD.gn
index 4384ea21b7306cdd910c8d835e4224313eb51760..6ead4c71c74a72606066f48a2d67bf57a01915ea 100644
--- a/components/resources/BUILD.gn
+++ b/components/resources/BUILD.gn
@@ -64,12 +64,9 @@ compress_file_brotli("compressed_about_credits") {
 
 action("about_credits") {
   script = "//tools/licenses.py"
+  depfile = "$target_gen_dir/$target_name.d"
 
   inputs = [
-    # This is not a complete list. TODO(phajdan.jr, dbeam): licenses.py needs to
-    # generate a .d file with all the licenses/credits that about:credits uses.
-    # Then about:credits will automatically rebuild when one of them changes.
-    # See: depfile in gn's documentation (gn help depfile).
     "../about_ui/resources/about_credits.tmpl",
     "../about_ui/resources/about_credits_entry.tmpl",
   ]
@@ -80,6 +77,8 @@ action("about_credits") {
 
   args = [
     "--target-os=$target_os",
+    "--depfile",
+    rebase_path(depfile, root_build_dir),
     "credits",
     rebase_path(about_credits_file, root_build_dir),
   ]