Docserver: Persist stat cache for versioned file systems

chrome/common/extensions/docs/server2/gitiles_file_system.py

Index: chrome/common/extensions/docs/server2/gitiles_file_system.py
diff --git a/chrome/common/extensions/docs/server2/gitiles_file_system.py b/chrome/common/extensions/docs/server2/gitiles_file_system.py
index 2962235da84e6c0a1d6f71824ea7694e6a08883b..80d10b3c3301ceff2a3b2af425c940b67c6ee372 100644
--- a/chrome/common/extensions/docs/server2/gitiles_file_system.py
+++ b/chrome/common/extensions/docs/server2/gitiles_file_system.py
@@ -233,11 +233,11 @@ class GitilesFileSystem(FileSystem):
     return self._ResolveFetchContent(path, fetch_future).Then(stat)
 
   def GetIdentity(self):
-    # NOTE: Do not use commit information to create the string identity.
-    # Doing so will mess up caching.
-    if self._commit is None and self._branch != 'master':
+    if self._commit is not None:
+      str_id = '%s/%s/%s' % (GITILES_BASE, GITILES_SRC_ROOT, self._commit)
+    elif self._branch == 'master':
+      str_id = '%s/%s/master' % (GITILES_BASE, GITILES_SRC_ROOT)
+    else:
       str_id = '%s/%s/%s/%s' % (
           GITILES_BASE, GITILES_SRC_ROOT, GITILES_BRANCHES_PATH, self._branch)
-    else:
-      str_id = '%s/%s' % (GITILES_BASE, GITILES_SRC_ROOT)
     return '@'.join((self.__class__.__name__, StringIdentity(str_id)))