Use the ThreadPool for all isolates and native ports. Previously,

runtime/vm/vm_sources.gypi

 # Copyright (c) 2012, 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.
 
 # This file contains all sources (vm and tests) for the dart virtual machine.
 # Unit test files need to have a '_test' suffix appended to the name.
 {
   'sources': [
     'allocation.cc',
     'allocation.h',
@@ skipping 154 matching lines @@
     'json_test.cc',
     'longjump.cc',
     'longjump.h',
     'longjump_test.cc',
     'memory_region.cc',
     'memory_region.h',
     'memory_region_test.cc',
     'message.cc',
     'message.h',
     'message_test.cc',
+    'message_handler.cc',
+    'message_handler.h',
+    'message_handler_test.cc',
     'native_arguments.cc',
     'native_arguments.h',
     'native_entry.cc',
     'native_entry.h',
     'native_entry_test.cc',
     'native_entry_test.h',
     'native_message_handler.cc',
     'native_message_handler.h',
     'object.cc',
     'object.h',
@@ skipping 86 matching lines @@
     'virtual_memory_test.cc',
     'virtual_memory_win.cc',
     'verifier.cc',
     'verifier.h',
     'visitor.h',
     'zone.cc',
     'zone.h',
     'zone_test.cc',
   ],
 }