Refactor the python system_impl module.

mojo/public/python/mojo/system_impl.pyx

Index: mojo/public/python/mojo/system_impl.pyx
diff --git a/mojo/public/python/mojo/system_impl.pyx b/mojo/public/python/mojo/system_impl.pyx
index 6e79c51b0e7421cca16adb508914afbc579aba51..1e5d3f6d4f442dcaeef850912e190d93e94fa265 100644
--- a/mojo/public/python/mojo/system_impl.pyx
+++ b/mojo/public/python/mojo/system_impl.pyx
@@ -6,10 +6,12 @@
 
 cimport c_core
 cimport c_environment
+cimport c_async_waiter
 
 
 from libc.stdint cimport uintptr_t
 
+
 def SetSystemThunks(system_thunks_as_object):
   """Bind the basic Mojo Core functions.
   """
@@ -53,13 +55,13 @@ cdef class RunLoop(object):
 
 # We use a wrapping class to be able to call the C++ class PythonAsyncWaiter
 # across module boundaries.
-cdef class _AsyncWaiter(object):
+cdef class AsyncWaiter(object):
   cdef c_environment.CEnvironment* _cenvironment
-  cdef c_environment.PythonAsyncWaiter* _c_async_waiter
+  cdef c_async_waiter.PythonAsyncWaiter* _c_async_waiter
 
   def __init__(self):
     self._cenvironment = new c_environment.CEnvironment()
-    self._c_async_waiter = new c_environment.PythonAsyncWaiter()
+    self._c_async_waiter = c_environment.NewAsyncWaiter()
 
   def __dealloc__(self):
     del self._c_async_waiter
@@ -70,6 +72,3 @@ cdef class _AsyncWaiter(object):
 
   def CancelWait(self, wait_id):
     self._c_async_waiter.CancelWait(wait_id)
-
-
-ASYNC_WAITER = _AsyncWaiter()