Enable concurrent optimization test after migrating scopes to Thread*

runtime/vm/longjump.cc

Index: runtime/vm/longjump.cc
diff --git a/runtime/vm/longjump.cc b/runtime/vm/longjump.cc
index 563c64ba7edf539c0836215d2fa608ccc089730d..0e53b600ddfe21860fd8551db4d83c4f056107d4 100644
--- a/runtime/vm/longjump.cc
+++ b/runtime/vm/longjump.cc
@@ -26,14 +26,18 @@ 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)
-  Isolate* isolate = thread->isolate();
-  ASSERT(isolate->MutatorThreadIsCurrentThread());
   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()) {
+    // A helper thread does not execute Dart code, so it's safe to jump.
+    ASSERT(top_exit_frame_info == 0);
+    return true;
+  }
   return ((top_exit_frame_info == 0) || (jumpbuf_addr < top_exit_frame_info));
 }