Very simple version of Isolates.

runtime/vm/isolate.h

 // Copyright (c) 2013, 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_ISOLATE_H_
 #define VM_ISOLATE_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/thread.h"
@@ skipping 494 matching lines @@
   Isolate* new_isolate_;
   Isolate* saved_isolate_;
   uword saved_stack_limit_;
 
   DISALLOW_COPY_AND_ASSIGN(SwitchIsolateScope);
 };
 
 
 class IsolateSpawnState {
  public:
-  IsolateSpawnState(const Function& func, const Function& callback_func);
+  explicit IsolateSpawnState(const Function& func);
   explicit IsolateSpawnState(const char* script_url);
   ~IsolateSpawnState();
 
   Isolate* isolate() const { return isolate_; }
   void set_isolate(Isolate* value) { isolate_ = value; }
   char* script_url() const { return script_url_; }
   char* library_url() const { return library_url_; }
   char* function_name() const { return function_name_; }
   char* exception_callback_name() const { return exception_callback_name_; }
 
   RawObject* ResolveFunction();
   void Cleanup();
 
  private:
   Isolate* isolate_;
   char* script_url_;
   char* library_url_;
   char* function_name_;
   char* exception_callback_name_;
 };
 
 }  // namespace dart
 
 #endif  // VM_ISOLATE_H_