Track async causal stack traces

runtime/vm/intrinsifier_arm64.cc

 // Copyright (c) 2014, 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.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_ARM64.
 #if defined(TARGET_ARCH_ARM64)
 
 #include "vm/intrinsifier.h"
 
 #include "vm/assembler.h"
@@ skipping 2349 matching lines @@
   __ ldr(R0, Address(THR, Thread::dart_stream_offset()));
   // Load uintptr_t from TimelineStream*.
   __ ldr(R0, Address(R0, TimelineStream::enabled_offset()));
   __ cmp(R0, Operand(0));
   __ LoadObject(R0, Bool::False());
   __ LoadObject(TMP, Bool::True());
   __ csel(R0, TMP, R0, NE);
   __ 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