chromeos: Concatenate D-Bus busconfig files

To reduce disk space usage and disk IO during startup.

In Chrome OS, chromeos-chrome ebuild installs chrome.conf busconfig file whose only contents is:
  <includedir>/opt/google/chrome/dbus</includedir>

concat_dbus_conf_files.py concatenates busconfig files in /opt/google/chrome/dbus by merging each conf file's <busconfig> into one.
This is exactly the same thing as what <includedir> tag in chrome.conf does so there should be no functional changes.

Before this CL: chrome.conf includes 17 busconfig files in /opt/google/chrome/dbus
After this CL: chrome.conf includes only 2 files (i.e. chrome_dbus_services.conf and ash_dbus_services.conf).

BUG=1020044
TEST=Manually confirmed the contents of out.conf after running chromeos/tools/concat_dbus_conffiles.py out.conf ash/dbus/*.conf
TEST=Chrome boots after replacing the contents of /opt/google/chrome/dbus
TEST=Can call org.chromium.LivenessServiceInterface.CheckLiveness with dbus-send

Change-Id: Id0e572c2834a6ebec8f2e385bfbe6d1ee67fc37c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1895021
Commit-Queue: Ryo Hashimoto <hashimoto@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#713750}

ash/BUILD.gn

@@ -1645,16 +1645,21 @@ static_library("ash_shell_lib_with_content") {
   ]
 }
 
-copy("dbus_service_files") {
+action("dbus_service_files") {
   sources = [
     "dbus/org.chromium.DisplayService.conf",
     "dbus/org.chromium.GesturePropertiesService.conf",
     "dbus/org.chromium.LivenessService.conf",
     "dbus/org.chromium.UrlHandlerService.conf",
   ]
+  output_conf_file = "$root_out_dir/dbus/ash_dbus_services.conf"
   outputs = [
-    "$root_out_dir/dbus/{{source_file_part}}",
+    output_conf_file,
   ]
+
+  script = "//chromeos/tools/concat_dbus_conf_files.py"
+  args = [ rebase_path(output_conf_file, root_build_dir) ]
+  args += rebase_path(sources, root_build_dir)
 }
 
 test("ash_unittests") {

chrome/browser/chromeos/BUILD.gn

@@ -2337,7 +2337,7 @@ source_set("chromeos") {
   }
 }
 
-copy("dbus_service_files") {
+action("dbus_service_files") {
   sources = [
     "dbus/org.chromium.ChromeFeaturesService.conf",
     "dbus/org.chromium.ComponentUpdaterService.conf",
@@ -2353,9 +2353,14 @@ copy("dbus_service_files") {
     "dbus/org.chromium.VirtualFileRequestService.conf",
     "dbus/org.chromium.VmApplicationsService.conf",
   ]
+  output_conf_file = "$root_out_dir/dbus/chrome_dbus_services.conf"
   outputs = [
-    "$root_out_dir/dbus/{{source_file_part}}",
+    output_conf_file,
   ]
+
+  script = "//chromeos/tools/concat_dbus_conf_files.py"
+  args = [ rebase_path(output_conf_file, root_build_dir) ]
+  args += rebase_path(sources, root_build_dir)
 }
 
 static_library("arc_test_support") {

chromeos/tools/concat_dbus_conf_files.py

@@ -0,0 +1,43 @@
+#!/usr/bin/env python
+# Copyright 2019 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.
+
+"""Concatenates D-Bus busconfig files."""
+
+import sys
+import xml.etree.ElementTree
+
+
+_BUSCONFIG_FILE_HEADER="""<!DOCTYPE busconfig
+  PUBLIC "-//freedesktop//DTD D-Bus Bus Configuration 1.0//EN"
+  "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
+"""
+
+
+def main():
+  if len(sys.argv) < 3:
+    sys.stderr.write('Usage: %s OUTFILE INFILES\n' % (sys.argv[0]))
+    sys.exit(1)
+
+  out_path = sys.argv[1]
+  in_paths = sys.argv[2:]
+
+  # Parse the first input file.
+  tree = xml.etree.ElementTree.parse(in_paths[0])
+  assert(tree.getroot().tag == 'busconfig')
+
+  # Append the remaining input files to the first file.
+  for path in in_paths[1:]:
+    current_tree = xml.etree.ElementTree.parse(path)
+    assert(current_tree.getroot().tag == 'busconfig')
+    for child in current_tree.getroot():
+      tree.getroot().append(child)
+
+  # Output the result.
+  with open(out_path, "w") as f:
+    f.write(_BUSCONFIG_FILE_HEADER)
+    tree.write(f)
+
+if __name__ == '__main__':
+  main()