unbundle: add replace_gn_files.py and unbundled GN file for libxml

build/linux/unbundle/replace_gn_files.py

Index: build/linux/unbundle/replace_gn_files.py
diff --git a/build/linux/unbundle/replace_gn_files.py b/build/linux/unbundle/replace_gn_files.py
new file mode 100755
index 0000000000000000000000000000000000000000..196ee2fbbd3283ed45bfc15f52ae8be16cb726d8
--- /dev/null
+++ b/build/linux/unbundle/replace_gn_files.py
@@ -0,0 +1,65 @@
+#!/usr/bin/env python
+# Copyright 2016 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.
+
+"""
+Replaces GN files in tree with files from here that
+make the build use system libraries.
+"""
+
+from __future__ import print_function
+
+import argparse
+import os
+import shutil
+import sys
+
+
+REPLACEMENTS = {
+  'libxml': 'third_party/libxml/BUILD.gn',
+}
+
+
+def DoMain(argv):
+  my_dirname = os.path.dirname(__file__)
+  source_tree_root = os.path.abspath(
+    os.path.join(my_dirname, '..', '..', '..'))
+
+  parser = argparse.ArgumentParser()
+  parser.add_argument('--system-libraries', nargs='*', default=[])
+  parser.add_argument('--undo', action='store_true')
+
+  args = parser.parse_args(argv)
+
+  handled_libraries = set()
+  for lib, path in REPLACEMENTS.items():
+    if lib not in args.system_libraries:
+      continue
+    handled_libraries.add(lib)
+
+    if args.undo:
+      # Restore original file, and also remove the backup.
+      # This is meant to restore the source tree to its original state.
+      os.rename(os.path.join(source_tree_root, path + '.orig'),
+                os.path.join(source_tree_root, path))
+    else:
+      # Create a backup copy for --undo.
+      shutil.copyfile(os.path.join(source_tree_root, path),
+                      os.path.join(source_tree_root, path + '.orig'))
+
+      # Copy the GN file from directory of this script to target path.
+      shutil.copyfile(os.path.join(my_dirname, '%s.gn' % lib),
+                      os.path.join(source_tree_root, path))
+
+  unhandled_libraries = set(args.system_libraries) - handled_libraries
+  if unhandled_libraries:
+    print('Unrecognized system libraries requested: %s' % ', '.join(
+        sorted(unhandled_libraries)), file=sys.stderr)
+    return 1
+
+  return 0
+
+
+if __name__ == '__main__':
+  sys.exit(DoMain(sys.argv[1:]))