Track async causal stack traces

runtime/vm/intrinsifier_arm.cc

Index: runtime/vm/intrinsifier_arm.cc
diff --git a/runtime/vm/intrinsifier_arm.cc b/runtime/vm/intrinsifier_arm.cc
index 99205a75eaa1c5a0a009c1da69194ccb725a5dc7..4c5009b38d07d00dbcb26a61805770a2566bf350 100644
--- a/runtime/vm/intrinsifier_arm.cc
+++ b/runtime/vm/intrinsifier_arm.cc
@@ -2300,6 +2300,20 @@ 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_ARM