[Findit] Add a sub-pipeline to analyze failures caused by DEPS rolls.

appengine/findit/common/dependency.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.
 
+import collections
 
 class Dependency(object):
-  """Represent a dependency in Chrome, like blink, v8, pdfium, etc."""
-  def __init__(self, path, repo_url, revision, deps_file):
+  """Represents a dependency in Chrome, like blink, v8, pdfium, etc."""
+  def __init__(self, path, repo_url, revision, deps_file='DEPS'):
     self.path = path
     self.repo_url = repo_url
     self.revision = revision
     self.deps_file = deps_file
     self.parent = None
     self.children = dict()
 
   def SetParent(self, parent):
     assert self.parent is None
     self.parent = parent
     self.parent.AddChild(self)
 
   def AddChild(self, child):
     self.children[child.path] = child
 
   def ToDict(self):
     children_dict = {}
     for path, child in self.children.iteritems():
       children_dict[path] = child.ToDict()
     return {
         'path': self.path,
         'repo_url': self.repo_url,
         'revision': self.revision,
         'deps_file': self.deps_file,
         'children': children_dict,
     }
+
+
+class DependencyRoll(collections.namedtuple(
+    'DependencyRoll', ('path', 'repo_url', 'old_revision', 'new_revision'))):
+  """Represents a dependency roll (revision update) in chromium.
+
+  Note: It is possible that the DEPS roll is a revert so that |new_revision| is
+  actually older than |old_revision| in the dependency.
+  """
+
+  def ToDict(self):
+    return self._asdict()