Enable easy rebuild of native modules for unreleased electron (#12217)

* Enable easy rebuild of native modules for unreleased electron

Sometimes when developing locally (as I found this morning) you want to rebuild native modules
against an unreleased version of Electron (in this case local master).  This PR adds a simple
script to launch a local HTTP server that generates and hosts the required header and checksum
files to rebuild modules.  So far only tested on macOS but should work on all OS's

* Allow custom port

* clean up serve script

* make optionality more obvious

script/serve-node-headers.py

@@ -0,0 +1,56 @@
+#!/usr/bin/env python
+
+import argparse
+import atexit
+import os
+import shutil
+import sys
+import tarfile
+import time
+
+from subprocess import Popen, PIPE
+from lib.util import execute_stdout
+
+SOURCE_ROOT = os.path.abspath(os.path.dirname(os.path.dirname(__file__)))
+DIST_DIR    = os.path.join(SOURCE_ROOT, 'dist')
+
+
+def main():
+  args = parse_args()
+  header_dir = os.path.join(DIST_DIR, args.version)
+
+  # Generate Headers
+  script_path = os.path.join(SOURCE_ROOT, 'script', 'create-node-headers.py')
+  execute_stdout([sys.executable, script_path, '--version', args.version,
+                  '--directory', header_dir])
+
+  # Launch server
+  script_path = os.path.join(SOURCE_ROOT, 'node_modules', 'serve', 'bin',
+                            'serve.js')
+  server = Popen(['node', script_path, '--port=' + args.port], stdout=PIPE,
+                 cwd=DIST_DIR)
+  def cleanup():
+    server.kill()
+  atexit.register(cleanup)
+
+  time.sleep(1)
+
+  # Generate Checksums
+  script_path = os.path.join(SOURCE_ROOT, 'script', 'upload-node-checksums.py')
+  execute_stdout([sys.executable, script_path, '--version', args.version,
+                  '--dist-url', 'http://localhost:' + args.port,
+                  '--target-dir', header_dir])
+
+  print("Point your npm config at 'http://localhost:" + args.port + "'")
+  server.wait()
+
+def parse_args():
+  parser = argparse.ArgumentParser(description='create node header tarballs')
+  parser.add_argument('-v', '--version', help='Specify the version',
+                      required=True)
+  parser.add_argument('-p', '--port', help='Specify port to run local server',
+                      default='4321')
+  return parser.parse_args()
+
+if __name__ == '__main__':
+  sys.exit(main())