Add workaround where SVN.Revert() deletes the checkout.

checkout.py

 # coding=utf8
 # Copyright (c) 2012 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.
 """Manages a project checkout.
 
 Includes support for svn, git-svn and git.
 """
 
 import ConfigParser
@@ skipping 461 matching lines @@
           'Couldn\'t make sense out of svn commit message:\n' + out)
     return int(match.group(1))
 
   def _revert(self, revision):
     """Reverts local modifications or checks out if the directory is not
     present. Use depot_tools's functionality to do this.
     """
     flags = ['--ignore-externals']
     if revision:
       flags.extend(['--revision', str(revision)])
-    if not os.path.isdir(self.project_path):
+    if os.path.isdir(self.project_path):
+      # This may remove any part (or all) of the checkout.
+      scm.SVN.Revert(self.project_path, no_ignore=True)
+
+    if os.path.isdir(self.project_path):
+      # Revive files that were deleted in scm.SVN.Revert().
+      self._check_call_svn(['update', '--force'] + flags)
+    else:
       logging.info(
           'Directory %s is not present, checking it out.' % self.project_path)
       self._check_call_svn(
           ['checkout', self.svn_url, self.project_path] + flags, cwd=None)
-    else:
-      scm.SVN.Revert(self.project_path, no_ignore=True)
-      # Revive files that were deleted in scm.SVN.Revert().
-      self._check_call_svn(['update', '--force'] + flags)
     return self._get_revision()
 
   def _get_revision(self):
     out = self._check_output_svn(['info', '.'])
     revision = int(self._parse_svn_info(out, 'revision'))
     if revision != self._last_seen_revision:
       logging.info('Updated to revision %d' % revision)
       self._last_seen_revision = revision
     return revision
 
@@ skipping 223 matching lines @@
   def revisions(self, rev1, rev2):
     return self.checkout.revisions(rev1, rev2)
 
   @property
   def project_name(self):
     return self.checkout.project_name
 
   @property
   def project_path(self):
     return self.checkout.project_path