Fix case where an unmounted partition is accessed during tracing on Windows.

tools/isolate/trace_inputs.py

 #!/usr/bin/env python
 # coding=utf-8
 # Copyright (c) 2012 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.
 
 """Runs strace or dtrace on a test and processes the logs to extract the
 dependencies from the source tree.
 
 Automatically extracts directories where all the files are used to make the
@@ skipping 116 matching lines @@
             assert mapped not in self._MAPPING
             if mapped not in self._MAPPING:
               self._MAPPING[mapped] = letter
           except WindowsError:  # pylint: disable=E0602
             pass
 
     def to_dos(self, path):
       """Converts a native NT path to DOS path."""
       m = re.match(r'(^\\Device\\[a-zA-Z0-9]+)(\\.*)?$', path)
       assert m, path
-      assert m.group(1) in self._MAPPING, (path, self._MAPPING)
+      if not m.group(1) in self._MAPPING:
+        # Unmapped partitions may be accessed by windows for the
+        # fun of it while the test is running. Discard these.
+        return None
       drive = self._MAPPING[m.group(1)]
       if not drive or not m.group(2):
         return drive
       return drive + m.group(2)
 
 
 def get_native_path_case(root, relative_path):
   """Returns the native path case."""
   if sys.platform == 'win32':
     # Windows used to have an option to turn on case sensitivity on non Win32
@@ skipping 802 matching lines @@
             'New child: %d -> %d %s' % (ppid, pid, line[self.PROC_NAME]))
 
     def handle_SystemConfig_Any(self, line):
       pass
 
     def _handle_file(self, filename):
       """Handles a file that was touched.
 
       Interestingly enough, the file is always with an absolute path.
       """
-      if (self.blacklist(filename) or
+      if (not filename or
+          self.blacklist(filename) or
           os.path.isdir(filename) or
           filename in self.files or
           filename in self.non_existent):
         return
       logging.debug('_handle_file(%s)' % filename)
       if os.path.isfile(filename):
         self.files.add(filename)
       else:
         self.non_existent.add(filename)
 
@@ skipping 465 matching lines @@
       os.path.abspath(options.log),
       args,
       options.root_dir,
       options.cwd,
       options.product_dir,
       options.force)
 
 
 if __name__ == '__main__':
   sys.exit(main())