Move patch management functions into their own file, patch.py.

pending_manager.py

Index: pending_manager.py
diff --git a/pending_manager.py b/pending_manager.py
index df009233b37db00b35001aecf80c2029dfd88516..09310f68a78538b3163776c995aaf84283065f9c 100644
--- a/pending_manager.py
+++ b/pending_manager.py
@@ -25,6 +25,7 @@ import find_depot_tools  # pylint: disable=W0611
 import breakpad
 
 import model
+import patch
 from verification import base
 
 
@@ -38,20 +39,6 @@ def send_stack(e):
       maxlen=2000)
 
 
-def auto_mangle_git_patch(patch):
-  """Mangles a patch and automatically strip out git decoration."""
-  # Git patches have a/ at the beginning of source paths.  We strip that out
-  # with a regexp rather than the -p flag to patch so we can feed either Git
-  # or svn-style patches into the same apply command.  re.sub() should be used
-  # but flags=re.MULTILINE is only in python 2.7.
-  out = []
-  for line in patch.splitlines(True):
-    # TODO: It should just process the header lines.
-    out.append(re.sub(r'^--- a/', r'--- ',
-      re.sub(r'^\+\+\+ b/', r'+++ ', line)))
-  return ''.join(out)
-
-
 class PendingCommit(base.Verified):
   """Represents a pending commit that is being processed."""
   persistent = base.Verified.persistent + [
@@ -277,9 +264,9 @@ class PendingManager(object):
 
   def _apply_patch(self, pending, revision):
     """Applies the pending patch to the checkout and throws if it fails."""
-    patch = urllib2.urlopen(pending.patch_url()).read()
-    patch = auto_mangle_git_patch(patch)
-    if not self.checkout.apply_patch(patch):
+    patch_data = urllib2.urlopen(pending.patch_url()).read()
+    patch_data = patch.auto_mangle_git_patch(patch_data)
+    if not self.checkout.apply_patch(patch_data):
       raise base.DiscardPending(pending,
           'Patch failed to apply against %s.' % revision)