Add cleanup_links.py script that runs before sync.

This should reduce/eliminate the amount of manual cleanup users
have to do to sync past 177567c (#15754).

This is essentially a stripped down version of
https://chromium.googlesource.com/external/webrtc/+/526248779a6315b02f5ca36a2f76122d3914b67e/setup_links.py
which only does the link cleaning + adds removal of the links db.

BUG=webrtc:5006
NOTRY=True

Review-Url: https://codereview.webrtc.org/2603203002
Cr-Commit-Position: refs/heads/master@{#15897}

.gitignore

@@ -40,8 +40,6 @@
 /base
 /build
 /buildtools
-/links
-/links.db
 /mojo
 /out
 /testing

DEPS

@@ -138,6 +138,16 @@ deps_os = {
   },
 }
 
+pre_deps_hooks = [
+  {
+    # Remove any symlinks from before 177567c518b121731e507e9b9c4049c4dc96e4c8.
+    # TODO(kjellander): Remove this in March 2017.
+    'name': 'cleanup_links',
+    'pattern': '.',
+    'action': ['python', 'src/cleanup_links.py'],
+  },
+]
+
 hooks = [
   {
     # Check for legacy named top-level dir (named 'trunk').

cleanup_links.py

@@ -0,0 +1,104 @@
+#!/usr/bin/env python
+# Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
+#
+# Use of this source code is governed by a BSD-style license
+# that can be found in the LICENSE file in the root of the source
+# tree. An additional intellectual property rights grant can be found
+# in the file PATENTS.  All contributing project authors may
+# be found in the AUTHORS file in the root of the source tree.
+
+"""Script to cleanup symlinks created from setup_links.py.
+
+Before 177567c518b121731e507e9b9c4049c4dc96e4c8 (#15754) we had a Chromium
+checkout which we created symlinks into. In order to do clean syncs after
+landing that change, this script cleans up any old symlinks, avoiding annoying
+manual cleanup needed in order to complete gclient sync.
+"""
+
+import logging
+import optparse
+import os
+import shelve
+import subprocess
+import sys
+
+
+ROOT_DIR = os.path.dirname(os.path.abspath(__file__))
+LINKS_DB = 'links'
+
+# Version management to make future upgrades/downgrades easier to support.
+SCHEMA_VERSION = 1
+
+class WebRTCLinkSetup(object):
+  def __init__(self, links_db, dry_run=False):
+    self._dry_run = dry_run
+    self._links_db = links_db
+
+  def CleanupLinks(self):
+    logging.debug('CleanupLinks')
+    for source, link_path  in self._links_db.iteritems():
+      if source == 'SCHEMA_VERSION':
+        continue
+      if os.path.islink(link_path) or sys.platform.startswith('win'):
+        # os.path.islink() always returns false on Windows
+        # See http://bugs.python.org/issue13143.
+        logging.debug('Removing link to %s at %s', source, link_path)
+        if not self._dry_run:
+          if os.path.exists(link_path):
+            if sys.platform.startswith('win') and os.path.isdir(link_path):
+              subprocess.check_call(['rmdir', '/q', '/s', link_path],
+                                    shell=True)
+            else:
+              os.remove(link_path)
+          del self._links_db[source]
+
+
+def _initialize_database(filename):
+  links_database = shelve.open(filename)
+  # Wipe the database if this version of the script ends up looking at a
+  # newer (future) version of the links db, just to be sure.
+  version = links_database.get('SCHEMA_VERSION')
+  if version and version != SCHEMA_VERSION:
+    logging.info('Found database with schema version %s while this script only '
+                 'supports %s. Wiping previous database contents.', version,
+                 SCHEMA_VERSION)
+    links_database.clear()
+  links_database['SCHEMA_VERSION'] = SCHEMA_VERSION
+  return links_database
+
+
+def main():
+  parser = optparse.OptionParser()
+  parser.add_option('-d', '--dry-run', action='store_true', default=False,
+                    help='Print what would be done, but don\'t perform any '
+                         'operations. This will automatically set logging to '
+                         'verbose.')
+  parser.add_option('-v', '--verbose', action='store_const',
+                    const=logging.DEBUG, default=logging.INFO,
+                    help='Print verbose output for debugging.')
+  options, _ = parser.parse_args()
+
+  if options.dry_run:
+    options.verbose = logging.DEBUG
+  logging.basicConfig(format='%(message)s', level=options.verbose)
+
+  # Work from the root directory of the checkout.
+  script_dir = os.path.dirname(os.path.abspath(__file__))
+  os.chdir(script_dir)
+
+  # The database file gets .db appended on some platforms.
+  db_filenames = [LINKS_DB, LINKS_DB + '.db']
+  if any(os.path.isfile(f) for f in db_filenames):
+    links_database = _initialize_database(LINKS_DB)
+    try:
+      symlink_creator = WebRTCLinkSetup(links_database, options.dry_run)
+      symlink_creator.CleanupLinks()
+    finally:
+      for f in db_filenames:
+        if os.path.isfile(f):
+          os.remove(f)
+  return 0
+
+
+if __name__ == '__main__':
+  sys.exit(main())