Track async causal stack traces

runtime/vm/thread.h

Index: runtime/vm/thread.h
diff --git a/runtime/vm/thread.h b/runtime/vm/thread.h
index b680a4f1bf6f6800fe7d11e3c28682abed975194..fe245a6a0dfa58fd5c5c2fe89e08bba0ba9f4c2e 100644
--- a/runtime/vm/thread.h
+++ b/runtime/vm/thread.h
@@ -44,10 +44,12 @@ class RawObject;
 class RawCode;
 class RawError;
 class RawGrowableObjectArray;
+class RawStackTrace;
 class RawString;
 class RuntimeEntry;
 class Smi;
 class StackResource;
+class StackTrace;
 class String;
 class TimelineStream;
 class TypeArguments;
@@ -505,6 +507,14 @@ class Thread : public BaseThread {
   void set_sticky_error(const Error& value);
   void clear_sticky_error();
 
+  RawStackTrace* async_stack_trace() const;
+  void set_async_stack_trace(const StackTrace& stack_trace);
+  void set_raw_async_stack_trace(RawStackTrace* raw_stack_trace);
+  void clear_async_stack_trace();
+  static intptr_t async_stack_trace_offset() {
+    return OFFSET_OF(Thread, async_stack_trace_);
+  }
+
   CompilerStats* compiler_stats() { return compiler_stats_; }
 
 #if defined(DEBUG)
@@ -687,6 +697,7 @@ class Thread : public BaseThread {
   StoreBufferBlock* store_buffer_block_;
   uword vm_tag_;
   TaskKind task_kind_;
+  RawStackTrace* async_stack_trace_;
 // State that is cached in the TLS for fast access in generated code.
 #define DECLARE_MEMBERS(type_name, member_name, expr, default_init_value)      \
   type_name member_name;