Add infrastructure to download golang and build AppRTC collider.

build_mercurial_local.py

+#!/usr/bin/python
+# Copyright 2014 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.
+
+"""Builds a local mercurial (hg) copy.
+
+This is used by the go toolchain.
+"""
+
+import os
+import shutil
+import subprocess
+import sys
+
+import utils
+
+
+def main():
+  if not os.path.exists('mercurial'):
+    return 'Expected mercurial at %s.' % os.path.abspath('mercurial')
+
+  os.chdir('mercurial')
+
+  if utils.GetPlatform() == 'win':
+    subprocess.check_call(['python', 'setup.py', '--pure', 'build_py', '-c',
+                           '-d', '.', 'build_ext',
+                           '-i', 'build_mo', '--force'])

[kjellander_chromium, 2014/12/08 13:58:08]

where does the local copy end up? 
Doesn't it need to be installed as well?
http://mercurial.selenic.com/wiki/WindowsInstall includes a second call to
setup.py with the "install" command.

[phoglund_chromium, 2014/12/08 14:26:16]

This makes the mercurial/hg python script work. It won't work before this call
is made. Install installs hg on the system (I think), which we don't want. We
just want hg to work when golang calls it.

+    with open('hg.bat', 'w') as put_hg_in_path:
+      # Write a hg.bat since the go toolchain expects to find something called
+      # 'hg' in the path, but Windows only recognizes executables ending with
+      # an extension in PATHEXT. Writing hg.bat effectively makes 'hg' callable

[kjellander_chromium, 2014/12/08 13:58:08]

Maybe it would be easiert to add "py" to the PATHEXT variable in an environment
copy and pass it into the make call below instead?

[phoglund_chromium, 2014/12/08 14:26:16]

No, it's not the make that needs hg, it's golang when we build the collider that
needs it. That's the next script. I considered adding .PY to PATHEXT but that
won't help since hg doesn't have the ending .py, even though it's a python
script. You can't put "no extension" into PATHEXT.

+      # if the mercurial folder is in PATH.
+      mercurial_path = os.path.abspath('hg')
+      put_hg_in_path.write('python %s %%*' % mercurial_path)
+  else:
+    subprocess.check_call(['make', 'local'])
+
+if __name__ == '__main__':
+  sys.exit(main())