Remove fake isolate from concurrent sweeper and extend lifetime of VM threads.

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 111 matching lines @@
 
   static inline Isolate* Current() {
     Thread* thread = Thread::Current();
     return thread == NULL ? NULL : thread->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 529 matching lines @@
 
   static void VisitIsolates(IsolateVisitor* visitor);
 
   Counters* counters() { return &counters_; }
 
   // Handle service messages until we are told to resume execution.
   void PauseEventHandler();
 
  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 272 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_