Issue 5913 - call correct npm executable on Win

ensure_dependencies.py

 #!/usr/bin/env python
 
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 import sys
 import os
 import posixpath
 import re
@@ skipping 260 matching lines @@
             return
     except IOError:
         return
 
     try:
         # Create an empty file, which gets deleted after successfully
         # installing Node.js dependencies.
         lockfile_path = os.path.join(target, NPM_LOCKFILE)
         open(lockfile_path, 'a').close()
 
-        cmd = ['npm', 'install', '--only=production', '--loglevel=warn',
+        if os.name == 'nt':
+            # Windows' CreateProcess() (called by subprocess.Popen()) only
+            # resolves executables ending in .exe. The windows installation of
+            # Node.js only provides a npm.cmd, which is executable but won't
+            # be recognized as such by CreateProcess().
+            npm_exec = 'npm.cmd'
+        else:
+            npm_exec = 'npm'
+
+        cmd = [npm_exec, 'install', '--only=production', '--loglevel=warn',
                '--no-package-lock', '--no-optional']
         subprocess.check_output(cmd, cwd=target)
 
         repo_types[vcs].ignore(os.path.join(target, NPM_LOCKFILE), target)
         repo_types[vcs].ignore(os.path.join(target, 'node_modules'), target)
 
         os.remove(lockfile_path)
     except OSError as e:
         import errno
         if e.errno == errno.ENOENT:
@@ skipping 137 matching lines @@
     args = parser.parse_args()
 
     if args.quiet:
         logging.disable(logging.INFO)
 
     repos = args.repos
     if not len(repos):
         repos = [os.path.dirname(__file__)]
     for repo in repos:
         resolve_deps(repo)