<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def FindMessageTypeByName(self, full_name):
 """Loads the named descriptor from the pool. Args: full_name: The full name of the descriptor to load. Returns: The descriptor for the named type. Raises: KeyError: if the message cannot be found in the pool. """


    full_name = _NormalizeFullyQualifiedName(full_name)
    if full_name not in self._descriptors:
      self._FindFileContainingSymbolInDb(full_name)
    return self._descriptors[full_name]