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

runtime/vm/dart.h

 // Copyright (c) 2011, 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.
 
 #ifndef VM_DART_H_
 #define VM_DART_H_
 
 #include "include/dart_api.h"
 #include "vm/allocation.h"
 
 namespace dart {
 
 // Forward declarations.
 class DebugInfo;
 class Isolate;
 class RawError;
+class ThreadPool;
 
 class Dart : public AllStatic {
  public:
   static bool InitOnce(Dart_IsolateCreateCallback create,
                        Dart_IsolateInterruptCallback interrupt);
 
   static Isolate* CreateIsolate(const char* name_prefix);
   static RawError* InitializeIsolate(const uint8_t* snapshot, void* data);
   static void ShutdownIsolate();
 
   static Isolate* vm_isolate() { return vm_isolate_; }
+  static ThreadPool* thread_pool() { return thread_pool_; }
 
   static void set_pprof_symbol_generator(DebugInfo* value) {
     pprof_symbol_generator_ = value;
   }
   static DebugInfo* pprof_symbol_generator() { return pprof_symbol_generator_; }
 
  private:
   static Isolate* vm_isolate_;
+  static ThreadPool* thread_pool_;
   static DebugInfo* pprof_symbol_generator_;
 };
 
 }  // namespace dart
 
 #endif  // VM_DART_H_