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

runtime/vm/exceptions.h

 // Copyright (c) 2011, 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.
 
 #ifndef RUNTIME_VM_EXCEPTIONS_H_
 #define RUNTIME_VM_EXCEPTIONS_H_
 
 #include "vm/allocation.h"
 #include "vm/token_position.h"
 
@@ skipping 81 matching lines @@
   DISALLOW_COPY_AND_ASSIGN(Exceptions);
 };
 
 // The index into the ExceptionHandlers table corresponds to
 // the try_index of the handler.
 struct ExceptionHandlerInfo {
   uint32_t handler_pc_offset;  // PC offset value of handler.
   int16_t outer_try_index;     // Try block index of enclosing try block.
   int8_t needs_stacktrace;     // True if a stacktrace is needed.
   int8_t has_catch_all;        // Catches all exceptions.
+  int8_t is_generated;         // True if this is a generated handler.
 };
 
 }  // namespace dart
 
 #endif  // RUNTIME_VM_EXCEPTIONS_H_