Change "NoneType" to "None". Add missing imports.

python3/_tracemalloc.py

@@ -3,12 +3,14 @@
 # for a more percise manual annotation of this module.
 # Feel free to edit the source below, but remove this header when you do.
 
+from typing import List, Tuple, Dict, Undefined, GenericType
+
 def _get_object_traceback(*args, **kwargs) -> object: pass
 
 def _get_traces() -> object:
     raise MemoryError()
 
-def clear_traces() -> NoneType: pass
+def clear_traces() -> None: pass
 
 def get_traceback_limit() -> long: pass
 
@@ -18,7 +20,7 @@ def get_tracemalloc_memory() -> object: pass
 
 def is_tracing() -> bool: pass
 
-def start(*args, **kwargs) -> NoneType:
+def start(*args, **kwargs) -> None:
     raise ValueError()
 
-def stop() -> NoneType: pass
+def stop() -> None: pass