[MD WebUI] Use html_out_file as prefix for depfile.

chrome/browser/resources/vulcanize.gni

 # Copyright 2017 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.
 
 template("node") {
   action(target_name) {
     forward_variables_from(invoker, "*")
 
     # Declare dependencies to all involved tools.
     inputs += [
@@ skipping 16 matching lines @@
 
 template("vulcanize") {
   node(target_name) {
     script = "//chrome/browser/resources/vulcanize_gn.py"
 
     inputs = [
       "//chrome/browser/resources/unpack_pak.py",
     ]
 
     # This depfile is generated by vulcanize_gn.py
-    depfile = "${target_gen_dir}/${target_name}.d"
+    depfile = "${target_gen_dir}/${invoker.html_out_file}.d"
 
     outputs = [
       "$target_gen_dir/${invoker.html_out_file}",
       "$target_gen_dir/${invoker.js_out_file}",
     ]
     deps = invoker.deps
 
     # Note that we have to manually pass the sources to our script if the
     # script needs them as inputs.
     args = [
@@ skipping 43 matching lines @@
 
     deps = invoker.deps
 
     args = [
              "--out_folder",
              rebase_path(target_gen_dir, root_build_dir),
              "--input_files",
            ] + invoker.input_files + [ "--output_files" ] + invoker.output_files
   }
 }