Added 'git-retry' bootstrap

git_common.py

 # Copyright 2014 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.
 
 # Monkeypatch IMapIterator so that Ctrl-C can kill everything properly.
 # Derived from https://gist.github.com/aljungberg/626518
 import multiprocessing.pool
 from multiprocessing.pool import IMapIterator
 def wrapper(func):
   def wrap(self, timeout=None):
@@ skipping 24 matching lines @@
 TEST_MODE = False
 
 FREEZE = 'FREEZE'
 FREEZE_SECTIONS = {
   'indexed': 'soft',
   'unindexed': 'mixed'
 }
 FREEZE_MATCHER = re.compile(r'%s.(%s)' % (FREEZE, '|'.join(FREEZE_SECTIONS)))
 
 
+# Retry a git operation if git returns a error response with any of these
+# messages. It's all observed 'bad' GoB responses so far.
+#
+# This list is inspired/derived from the one in ChromiumOS's Chromite:
+# <CHROMITE>/lib/git.py::GIT_TRANSIENT_ERRORS
+#
+# It was last imported from '7add3ac29564d98ac35ce426bc295e743e7c0c02'.
+GIT_TRANSIENT_ERRORS = (
+    # crbug.com/285832
+    r'! \[remote rejected\].*\(error in hook\)',
+
+    # crbug.com/289932
+    r'! \[remote rejected\].*\(failed to lock\)',
+
+    # crbug.com/307156
+    r'! \[remote rejected\].*\(error in Gerrit backend\)',
+
+    # crbug.com/285832
+    r'remote error: Internal Server Error',
+
+    # crbug.com/294449
+    r'fatal: Couldn\'t find remote ref ',
+
+    # crbug.com/220543
+    r'git fetch_pack: expected ACK/NAK, got',
+
+    # crbug.com/189455
+    r'protocol error: bad pack header',
+
+    # crbug.com/202807
+    r'The remote end hung up unexpectedly',
+
+    # crbug.com/298189
+    r'TLS packet with unexpected length was received',
+
+    # crbug.com/187444
+    r'RPC failed; result=\d+, HTTP code = \d+',
+
+    # crbug.com/315421
+    r'The requested URL returned error: 500 while accessing',
+
+    # crbug.com/388876
+    r'Connection timed out',
+)
+
+GIT_TRANSIENT_ERRORS_RE = re.compile('|'.join(GIT_TRANSIENT_ERRORS),
+                                     re.IGNORECASE)
+
+
 class BadCommitRefException(Exception):
   def __init__(self, refs):
     msg = ('one of %s does not seem to be a valid commitref.' %
            str(refs))
     super(BadCommitRefException, self).__init__(msg)
 
 
 def memoize_one(**kwargs):
   """Memoizes a single-argument pure function.
 
@@ skipping 604 matching lines @@
     return None
   return ret
 
 
 def upstream(branch):
   try:
     return run('rev-parse', '--abbrev-ref', '--symbolic-full-name',
                branch+'@{upstream}')
   except subprocess2.CalledProcessError:
     return None