Renames the isolate's mutator_thread_ to scheduled_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 200 matching lines @@
   }
   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;
-  }
+  bool IsMutatorThreadScheduled() { return scheduled_mutator_thread_ != NULL; }
 
   const char* name() const { return name_; }
 
 #if !defined(PRODUCT)
   const char* debugger_name() const { return debugger_name_; }
   void set_debugger_name(const char* name);
 #endif  // !defined(PRODUCT)
 
   int64_t UptimeMicros() const;
 
@@ skipping 827 matching lines @@
   intptr_t* spawn_count_;
 
   Dart_IsolateFlags isolate_flags_;
   bool paused_;
   bool errors_are_fatal_;
 };
 
 }  // namespace dart
 
 #endif  // RUNTIME_VM_ISOLATE_H_