Docserver: Add more skip_not_found support and cache "not found"s

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

 #!/usr/bin/env python
 # Copyright 2013 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 functools
 import os
 
 from compiled_file_system import CompiledFileSystem
 from copy import deepcopy
@@ skipping 182 matching lines @@
     self.assertTrue(*mock_fs.CheckAndReset())
 
     # Similar configuration to the 'apps/' case but deeper.
     future = compiled_fs.GetFromFileListing('')
     self.assertTrue(*mock_fs.CheckAndReset(stat_count=1,
                                            read_count=2,
                                            read_resolve_count=1))
     future.Get()
     self.assertTrue(*mock_fs.CheckAndReset(read_count=2, read_resolve_count=3))
 
+  def testSkipNotFound(self):
+    mock_fs = MockFileSystem(TestFileSystem(_TEST_DATA))
+    compiled_fs = CompiledFileSystem.Factory(
+        ObjectStoreCreator.ForTest()).Create(
+            mock_fs, lambda path, contents: contents, type(self))
+
+    future = compiled_fs.GetFromFile('no_file', skip_not_found=True)
+    # If the file doesn't exist, then the file system is not read.
+    self.assertTrue(*mock_fs.CheckAndReset(read_count=1, stat_count=1))
+    self.assertEqual(None, future.Get())
+    self.assertTrue(*mock_fs.CheckAndReset(read_resolve_count=1))
+    future = compiled_fs.GetFromFile('no_file', skip_not_found=True)
+    self.assertTrue(*mock_fs.CheckAndReset(stat_count=1))
+    self.assertEqual(None, future.Get())
+    # The result for a non-existent file should still be cached.
+    self.assertTrue(*mock_fs.CheckAndReset())
+    future = compiled_fs.GetFromFile('no_file')
+    self.assertRaises(FileNotFoundError, future.Get)
 
 
 if __name__ == '__main__':
   unittest.main()