DOM libraries generation should not fail when database cache don't exist.

lib/dom/scripts/database.py

 #!/usr/bin/python
 # Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 """Module to manage IDL files."""
 
 import copy
 import pickle
 import logging
@@ skipping 114 matching lines @@
   def Cache(self):
     """Serialize the database using pickle for faster startup in the future
     """
     output_file = open(os.path.join(self._root_dir, 'cache.pickle'), 'wb')
     pickle.dump(self._all_interfaces, output_file)
     pickle.dump(self._interfaces_to_delete, output_file)
 
   def LoadFromCache(self):
     """Deserialize the database using pickle for fast startup
     """
-    input_file = open(os.path.join(self._root_dir, 'cache.pickle'), 'rb')
+    input_file_name = os.path.join(self._root_dir, 'cache.pickle')
+    if not os.path.isfile(input_file_name):
+      self.Load()
+      return
+    input_file = open(input_file_name, 'rb')
     self._all_interfaces = pickle.load(input_file)
     self._interfaces_to_delete = pickle.load(input_file)
+    input_file.close()
 
   def Save(self):
     """Saves all in-memory interfaces into files."""
     for interface in self._all_interfaces.values():
       self._SaveInterfaceFile(interface)
     for interface_name in self._interfaces_to_delete:
       self._DeleteInterfaceFile(interface_name)
 
   def _SaveInterfaceFile(self, interface):
     """Saves an interface into the database.
@@ skipping 65 matching lines @@
       raise RuntimeError('Interface %s not found' % interface_name)
     self._interfaces_to_delete.append(interface_name)
     del self._all_interfaces[interface_name]
 
   def _DeleteInterfaceFile(self, interface_name):
     """Actual file deletion"""
     file_path = self._FilePath(interface_name)
     if os.path.exists(file_path):
       _logger.debug('deleting %s' % file_path)
       os.remove(file_path)