Revert "Eliminate fake-Isolate workaround from concurrent sweeper."

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 "vm/base_isolate.h"
@@ skipping 109 matching lines @@
   static inline Isolate* Current() {
     return reinterpret_cast<Isolate*>(OSThread::GetThreadLocal(isolate_key));
   }
 
   static void SetCurrent(Isolate* isolate);
 
   static void InitOnce();
   static Isolate* Init(const char* name_prefix, bool is_vm_isolate = false);
   void Shutdown();
 
+  Isolate* ShallowCopy();
+
   // Register a newly introduced class.
   void RegisterClass(const Class& cls);
   void RegisterClassAt(intptr_t index, const Class& cls);
   void ValidateClassTable();
 
   // Visit all object pointers.
   void VisitObjectPointers(ObjectPointerVisitor* visitor,
                            bool visit_prologue_weak_persistent_handles,
                            bool validate_frames);
 
@@ skipping 498 matching lines @@
   }
   REUSABLE_HANDLE_LIST(REUSABLE_HANDLE)
 #undef REUSABLE_HANDLE
 
   static void VisitIsolates(IsolateVisitor* visitor);
 
   Counters* counters() { return &counters_; }
 
  private:
   Isolate();
+  explicit Isolate(Isolate* original);
 
   void BuildName(const char* name_prefix);
   void PrintInvokedFunctions();
 
   void ProfileIdle();
 
   void set_user_tag(uword tag) {
     user_tag_ = tag;
   }
 
@@ skipping 251 matching lines @@
   uint8_t* serialized_args_;
   intptr_t serialized_args_len_;
   uint8_t* serialized_message_;
   intptr_t serialized_message_len_;
   bool paused_;
 };
 
 }  // namespace dart
 
 #endif  // VM_ISOLATE_H_