Track async causal stack traces

runtime/vm/intrinsifier_arm64.cc

Index: runtime/vm/intrinsifier_arm64.cc
diff --git a/runtime/vm/intrinsifier_arm64.cc b/runtime/vm/intrinsifier_arm64.cc
index 06f623e3b3f8d53bd0d03fbfed28896032cfa2ec..f580138edcdcd443d99289d6a7710b95e512e4ef 100644
--- a/runtime/vm/intrinsifier_arm64.cc
+++ b/runtime/vm/intrinsifier_arm64.cc
@@ -2367,6 +2367,20 @@ void Intrinsifier::Timeline_isDartStreamEnabled(Assembler* assembler) {
   __ ret();
 }
 
+
+void Intrinsifier::ClearAsyncThreadStackTrace(Assembler* assembler) {
+  __ LoadObject(R0, Object::null_object());
+  __ str(R0, Address(THR, Thread::async_stack_trace_offset()));
+  __ ret();
+}
+
+
+void Intrinsifier::SetAsyncThreadStackTrace(Assembler* assembler) {
+  __ ldr(R0, Address(THR, Thread::async_stack_trace_offset()));
+  __ LoadObject(R0, Object::null_object());
+  __ ret();
+}
+
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64