Add automatic retry on HTTP 502 for svn and connection drop for git.

scm.py

 # Copyright (c) 2006-2009 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 glob
 import os
 import re
 import shutil
@@ skipping 362 matching lines @@
           # way.
           failure.append(True)
 
       try:
         SVN.RunAndFilterOutput(args,
                                in_directory,
                                options.verbose,
                                True,
                                CaptureMatchingLines)
       except gclient_utils.Error:
-        # We enforce that some progress has been made.
-        if len(failure) and len(file_list) > previous_list_len:
+        # We enforce that some progress has been made or HTTP 502.
+        if ([True for f in failure if '502 Bad Gateway' in f] or
+            (len(failure) and len(file_list) > previous_list_len)):
           if args[0] == 'checkout':
-            args = args[:]
             # An aborted checkout is now an update.
-            args[0] = 'update'
+            args = ['update'] + args[1:]
           continue
-        # No progress was made, bail out.
+        # No progress was made or an unknown error we aren't sure, bail out.
         raise
       break
 
   @staticmethod
   def RunAndFilterOutput(args,
                          in_directory,
                          print_messages,
                          print_stdout,
                          filter):
     """Runs a command, optionally outputting to stdout.
@@ skipping 328 matching lines @@
     if not cur_dir_repo_root:
       return None
 
     while True:
       parent = os.path.dirname(directory)
       if (SVN.CaptureInfo(parent, print_error=False).get(
               "Repository Root") != cur_dir_repo_root):
         break
       directory = parent
     return GetCasedPath(directory)