[Findit] Factoring the gitiles (etc) stuff out into its own directory

appengine/findit/common/chromium_deps.py

Index: appengine/findit/common/chromium_deps.py
diff --git a/appengine/findit/common/chromium_deps.py b/appengine/findit/common/chromium_deps.py
index 39c63472fa5e4b9e3d052d27103ea0f746e9eb9d..794b32738414ec06ad8ffb93f0e343e2b4162e45 100644
--- a/appengine/findit/common/chromium_deps.py
+++ b/appengine/findit/common/chromium_deps.py
@@ -4,9 +4,17 @@
 
 import re
 
+# N.B., in order for our mocking framework to work correctly, we *must not*
+# import the GitRepository class directly; instead, we must only import
+# the git_repository module and then rely on dynamic dispatch to resolve
+# the module's GitRepository attribute. Otherwise the DEPSDownloader.Load
+# method will hold a reference directly to the real GitRepository class,
+# which means we can't swap it out for the DummyGitRepository class, which
+# in turn will cause some unit tests to fail (since we can't mock the
+# responses of doing SSL stuff).
+from lib.gitiles import git_repository
 from common import dependency
 from common import deps_parser
-from common import git_repository
 from common import http_client_appengine
 
 
@@ -30,6 +38,9 @@ def IsChromeVersion(revision):
 class DEPSDownloader(deps_parser.DEPSLoader):
   """Downloads DEPS from remote Git repo."""
 
+  # TODO(wrengr): why do we allocate a new GitRepository every time
+  # we call Load, rather than just doing it once and saving it in the
+  # DEPSDownloader class (via RAII)?
   def Load(self, repo_url, revision, deps_file):
     http_client = http_client_appengine.HttpClientAppengine()
     repo = git_repository.GitRepository(repo_url, http_client)