Docserver: there is only one.

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

Index: chrome/common/extensions/docs/server2/file_system.py
diff --git a/chrome/common/extensions/docs/server2/file_system.py b/chrome/common/extensions/docs/server2/file_system.py
index d8998263a04d47a7e9fdbc20b476a95c5cb54fa7..3226ebe8545353e9750615e0f90999b0ef527ae4 100644
--- a/chrome/common/extensions/docs/server2/file_system.py
+++ b/chrome/common/extensions/docs/server2/file_system.py
@@ -51,7 +51,7 @@ class FileSystem(object):
     and failing that as latin-1 (some extension docs use latin-1). If
     binary=True then the contents will be a str.
     '''
-    raise NotImplementedError()
+    raise NotImplementedError(self.__class__)
 
   def ReadSingle(self, path, binary=False):
     '''Reads a single file from the FileSystem.
@@ -64,7 +64,7 @@ class FileSystem(object):
     is a directory, |StatInfo| will have the versions of all the children of
     the directory in |StatInfo.child_versions|.
     '''
-    raise NotImplementedError()
+    raise NotImplementedError(self.__class__)
 
   def GetIdentity(self):
     '''The identity of the file system, exposed for caching classes to
@@ -73,7 +73,7 @@ class FileSystem(object):
     different to that of a SubversionFileSystem with a base path of /bar, is
     different to a LocalFileSystem with a base path of /usr.
     '''
-    raise NotImplementedError()
+    raise NotImplementedError(self.__class__)
 
   def Walk(self, root):
     '''Recursively walk the directories in a file system, starting with root.