Moves the top_ and end_ words of the Scavenger into mutator thread.

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 RUNTIME_VM_ISOLATE_H_
 #define RUNTIME_VM_ISOLATE_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/atomic.h"
@@ skipping 202 matching lines @@
 
   Dart_MessageNotifyCallback message_notify_callback() const {
     return message_notify_callback_;
   }
   void set_message_notify_callback(Dart_MessageNotifyCallback value) {
     message_notify_callback_ = value;
   }
 
   Thread* mutator_thread() const;
 
+  // Mutator thread is not scheduled if NULL or no heap is attached
+  // to it. The latter only occurs when the mutator thread object
+  // is unscheduled by the isolate (or never scheduled).
+  bool IsMutatorThreadScheduled() {
+    return mutator_thread_ != NULL && mutator_thread_->heap() != NULL;
+  }
+
   const char* name() const { return name_; }
   const char* debugger_name() const { return debugger_name_; }
   void set_debugger_name(const char* name);
 
   int64_t UptimeMicros() const;
 
   Dart_Port main_port() const { return main_port_; }
   void set_main_port(Dart_Port port) {
     ASSERT(main_port_ == 0);  // Only set main port once.
     main_port_ = port;
@@ skipping 801 matching lines @@
   intptr_t* spawn_count_;
 
   Dart_IsolateFlags isolate_flags_;
   bool paused_;
   bool errors_are_fatal_;
 };
 
 }  // namespace dart
 
 #endif  // RUNTIME_VM_ISOLATE_H_