Add IsMutatorThread to the Thread class and use it instead of MutatorThreadIsCurrentThread

runtime/vm/thread.h

 // Copyright (c) 2015, 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_THREAD_H_
 #define VM_THREAD_H_
 
 #include "vm/globals.h"
 #include "vm/handles.h"
 #include "vm/os_thread.h"
@@ skipping 143 matching lines @@
   ~Thread();
 
   // The topmost zone used for allocation in this thread.
   Zone* zone() const { return state_.zone; }
 
   // The isolate that this thread is operating on, or NULL if none.
   Isolate* isolate() const { return isolate_; }
   static intptr_t isolate_offset() {
     return OFFSET_OF(Thread, isolate_);
   }
+  bool IsMutatorThread() const;
 
   // The (topmost) CHA for the compilation in this thread.
   CHA* cha() const;
   void set_cha(CHA* value);
 
   int32_t no_callback_scope_depth() const {
     return no_callback_scope_depth_;
   }
 
   void IncrementNoCallbackScopeDepth() {
@@ skipping 355 matching lines @@
 };
 
 #if defined(TARGET_OS_WINDOWS)
 // Clears the state of the current thread and frees the allocation.
 void WindowsThreadCleanUp();
 #endif
 
 }  // namespace dart
 
 #endif  // VM_THREAD_H_