Track the 'awaiter return' call stack use it to detect uncaught exceptions in async functions

runtime/vm/flow_graph_builder.h

Index: runtime/vm/flow_graph_builder.h
diff --git a/runtime/vm/flow_graph_builder.h b/runtime/vm/flow_graph_builder.h
index 98819bc28d5fefa1f36c0f2f61abbd36d5e7a106..56ca9657cb71e77622ab80825e3b658923dcf3e4 100644
--- a/runtime/vm/flow_graph_builder.h
+++ b/runtime/vm/flow_graph_builder.h
@@ -172,6 +172,12 @@ class FlowGraphBuilder : public ValueObject {
   Isolate* isolate() const { return parsed_function().isolate(); }
   Zone* zone() const { return parsed_function().zone(); }
 
+  void AppendAwaitTokenPosition(TokenPosition token_pos);
+
+  ZoneGrowableArray<TokenPosition>* await_token_positions() const {
+    return await_token_positions_;
+  }
+
  private:
   friend class NestedStatement;  // Explicit access to nesting_stack_.
   friend class Intrinsifier;
@@ -212,6 +218,7 @@ class FlowGraphBuilder : public ValueObject {
 
   intptr_t jump_count_;
   ZoneGrowableArray<JoinEntryInstr*>* await_joins_;
+  ZoneGrowableArray<TokenPosition>* await_token_positions_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(FlowGraphBuilder);
 };