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

runtime/vm/longjump.cc

Index: runtime/vm/longjump.cc
diff --git a/runtime/vm/longjump.cc b/runtime/vm/longjump.cc
index e2cf726740e99e8f8b1a06119222774b13b9e530..0093375e19fafa55b1980c9825f2a2c67efbdacf 100644
--- a/runtime/vm/longjump.cc
+++ b/runtime/vm/longjump.cc
@@ -26,14 +26,13 @@ bool LongJumpScope::IsSafeToJump() {
   // We do not want to jump past Dart frames.  Note that this code
   // assumes the stack grows from high to low.
   Thread* thread = Thread::Current();
-  Isolate* isolate = thread->isolate();
   uword jumpbuf_addr = Isolate::GetCurrentStackPointer();
 #if defined(USING_SIMULATOR)
   uword top_exit_frame_info = isolate->simulator()->top_exit_frame_info();
 #else
   uword top_exit_frame_info = thread->top_exit_frame_info();
 #endif
-  if (!isolate->MutatorThreadIsCurrentThread()) {
+  if (!thread->IsMutatorThread()) {
     // A helper thread does not execute Dart code, so it's safe to jump.
     ASSERT(top_exit_frame_info == 0);
     return true;