Re-reland r245404 ("If the destination directory doesn't contain the desired repo, delete it")

scm.py

 # 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.
 
 """SCM-specific utility classes."""
 
 import cStringIO
 import glob
 import logging
 import os
@@ skipping 148 matching lines @@
   def GetBranchRef(cwd):
     """Returns the full branch reference, e.g. 'refs/heads/master'."""
     return GIT.Capture(['symbolic-ref', 'HEAD'], cwd=cwd)
 
   @staticmethod
   def GetBranch(cwd):
     """Returns the short branch name, e.g. 'master'."""
     return GIT.ShortBranchName(GIT.GetBranchRef(cwd))
 
   @staticmethod
-  def IsGitSvn(cwd):
+  def IsGitSvn(checkout_root):
     """Returns true if this repo looks like it's using git-svn."""
+    # A git-svn checkout has a .git directory.
+    if not os.path.isdir(os.path.join(checkout_root, '.git')):
+      return False
     # If you have any "svn-remote.*" config keys, we think you're using svn.
     try:
       GIT.Capture(['config', '--local', '--get-regexp', r'^svn-remote\.'],
-                  cwd=cwd)
+                  cwd=checkout_root)
       return True
     except subprocess2.CalledProcessError:
       return False
 
   @staticmethod
   def MatchSvnGlob(url, base_url, glob_spec, allow_wildcards):
     """Return the corresponding git ref if |base_url| together with |glob_spec|
     matches the full |url|.
 
     If |allow_wildcards| is true, |glob_spec| can contain wildcards (see below).
@@ skipping 216 matching lines @@
 
   @staticmethod
   def ParseGitSvnSha1(output):
     """Parses git-svn output for the first sha1."""
     match = re.search(r'[0-9a-fA-F]{40}', output)
     return match.group(0) if match else None
 
   @staticmethod
   def GetSha1ForSvnRev(cwd, rev):
     """Returns a corresponding git sha1 for a SVN revision."""
-    if not GIT.IsGitSvn(cwd=cwd):
+    if not GIT.IsGitSvn(cwd):
       return None
     try:
       output = GIT.Capture(['svn', 'find-rev', 'r' + str(rev)], cwd=cwd)
       return GIT.ParseGitSvnSha1(output)
     except subprocess2.CalledProcessError:
       return None
 
   @staticmethod
   def GetBlessedSha1ForSvnRev(cwd, rev):
     """Returns a git commit hash from the master branch history that has
@@ skipping 685 matching lines @@
         # revert, like for properties.
         if not os.path.isdir(cwd):
           # '.' was deleted. It's not worth continuing.
           return
         try:
           SVN.Capture(['revert', file_status[1]], cwd=cwd)
         except subprocess2.CalledProcessError:
           if not os.path.exists(file_path):
             continue
           raise