Update from https://crrev.com/304715

tools/clang/scripts/update.py

 #!/usr/bin/env python
 # 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.
 
 """Windows can't run .sh files, so this is a Python implementation of
 update.sh. This script should replace update.sh on all platforms eventually."""
 
 import os
 import re
 import shutil
 import subprocess
+import stat
 import sys
+import time
 
 # Do NOT CHANGE this if you don't know what you're doing -- see
 # https://code.google.com/p/chromium/wiki/UpdatingClang
 # Reverting problematic clang rolls is safe, though.
 # Note: this revision is only used for Windows. Other platforms use update.sh.
 LLVM_WIN_REVISION = 'HEAD'
 
 # ASan on Windows is useful enough to use it even while the clang/win is still
 # in bringup. Use a pinned revision to make it slightly more stable.
 if (re.search(r'\b(asan)=1', os.environ.get('GYP_DEFINES', '')) and
@@ skipping 27 matching lines @@
 
 
 def WriteStampFile(s):
   """Write s to the stamp file."""
   if not os.path.exists(LLVM_BUILD_DIR):
     os.makedirs(LLVM_BUILD_DIR)
   with open(STAMP_FILE, 'w') as f:
     f.write(s)
 
 
-def DeleteFiles(dir, pattern):
-  """Delete all files in dir matching pattern."""
-  n = 0
-  regex = re.compile(r'^' + pattern + r'$')
-  for root, _, files in os.walk(dir):
-    for f in files:
-      if regex.match(f):
-        os.remove(os.path.join(root, f))
-        n += 1
-  return n
+def RmTree(dir):
+  """Delete dir."""
+  def ChmodAndRetry(func, path, _):
+    # Subversion can leave read-only files around.
+    if not os.access(path, os.W_OK):
+      os.chmod(path, stat.S_IWUSR)
+      return func(path)
+    raise
+
+  shutil.rmtree(dir, onerror=ChmodAndRetry)
 
 
 def ClobberChromiumBuildFiles():
   """Clobber Chomium build files."""
   print 'Clobbering Chromium build files...'
   out_dir = os.path.join(CHROMIUM_DIR, 'out')
   if os.path.isdir(out_dir):
-    shutil.rmtree(out_dir)
+    RmTree(out_dir)
     print 'Removed Chromium out dir: %s.' % (out_dir)
 
 
-def RunCommand(command, tries=1):
-  """Run a command, possibly with multiple retries."""
-  for i in range(0, tries):
-    print 'Running %s (try #%d)' % (str(command), i + 1)
-    if subprocess.call(command, shell=True) == 0:
-      return
-    print 'Failed.'
-  sys.exit(1)
+def RunCommand(command, fail_hard=True):
+  """Run command and return success (True) or failure; or if fail_hard is
+     True, exit on failure."""
+
+  print 'Running %s' % (str(command))
+  if subprocess.call(command, shell=True) == 0:
+    return True
+  print 'Failed.'
+  if fail_hard:
+    sys.exit(1)
+  return False
 
 
 def CopyFile(src, dst):
   """Copy a file from src to dst."""
   shutil.copy(src, dst)
   print "Copying %s to %s" % (src, dst)
 
 
 def CopyDirectoryContents(src, dst, filename_filter=None):
   """Copy the files from directory src to dst
   with an optional filename filter."""
   if not os.path.exists(dst):
     os.makedirs(dst)
   for root, _, files in os.walk(src):
     for f in files:
       if filename_filter and not re.match(filename_filter, f):
         continue
       CopyFile(os.path.join(root, f), dst)
 
 
 def Checkout(name, url, dir):
   """Checkout the SVN module at url into dir. Use name for the log message."""
   print "Checking out %s r%s into '%s'" % (name, LLVM_WIN_REVISION, dir)
-  RunCommand(['svn', 'checkout', '--force',
-              url + '@' + LLVM_WIN_REVISION, dir], tries=2)
+
+  command = ['svn', 'checkout', '--force', url + '@' + LLVM_WIN_REVISION, dir]
+  if RunCommand(command, fail_hard=False):
+    return
+
+  if os.path.isdir(dir):
+    print "Removing %s." % (dir)
+    RmTree(dir)
+
+  print "Retrying."
+  RunCommand(command)
 
 
 def AddCMakeToPath():
   """Look for CMake and add it to PATH if it's not there already."""
   try:
     # First check if cmake is already on PATH.
     subprocess.call(['cmake', '--version'])
     return
   except OSError as e:
     if e.errno != os.errno.ENOENT:
@@ skipping 136 matching lines @@
 
   if re.search(r'\b(make_clang_dir)=', os.environ.get('GYP_DEFINES', '')):
     print 'Skipping Clang update (make_clang_dir= was set in GYP_DEFINES).'
     return 0
 
   return UpdateClang()
 
 
 if __name__ == '__main__':
   sys.exit(main())