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..20d3ce63ae702233310ccc3bba8e88ff4cd374eb 100644
--- a/chrome/common/extensions/docs/server2/gitiles_file_system.py
+++ b/chrome/common/extensions/docs/server2/gitiles_file_system.py
@@ -49,6 +49,10 @@ def _CreateStatInfo(json_data):
                   dict((e['name'], e['id']) for e in tree['entries']))
 
 
+def _CreateIdentityFromCommit(commit):
+  return '%s/%s/%s' % (GITILES_BASE, GITILES_SRC_ROOT, commit)
+
+
 class GitilesFileSystem(FileSystem):
   '''Class to fetch filesystem data from the Chromium project's gitiles
   service.
@@ -232,12 +236,21 @@ class GitilesFileSystem(FileSystem):
     fetch_future = self._FetchAsync(ToDirectory(dir_) + _JSON_FORMAT)
     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':
+  def GetStableIdentity(self):
+    '''The stable identity is always the same for GitilesFileSystems designated
+    to master, even if they are pinned to a specific commit'''
+    if self._branch == 'master':
+      str_id = '%s/%s/master' % (GITILES_BASE, GITILES_SRC_ROOT)
+    elif self._commit is not None:
+      str_id = _CreateIdentityFromCommit(self._commit)
+    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)))
+
+  def GetUnstableIdentity(self):
+    '''The unstable identity always tracks the commit ID if set.'''
+    if self._commit is not None:
+      return '@'.join((self.__class__.__name__, StringIdentity(
+          _CreateIdentityFromCommit(self._commit))))
+    return self.GetStableIdentity()