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

runtime/vm/flow_graph.cc

 // Copyright (c) 2012, 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/flow_graph.h"
 
 #include "vm/bit_vector.h"
 #include "vm/cha.h"
 #include "vm/flow_graph_builder.h"
 #include "vm/flow_graph_compiler.h"
@@ skipping 28 matching lines @@
       reverse_postorder_(),
       optimized_block_order_(),
       constant_null_(NULL),
       constant_dead_(NULL),
       constant_empty_context_(NULL),
       block_effects_(NULL),
       licm_allowed_(true),
       loop_headers_(NULL),
       loop_invariant_loads_(NULL),
       deferred_prefixes_(parsed_function.deferred_prefixes()),
+      await_token_positions_(NULL),
       captured_parameters_(new (zone()) BitVector(zone(), variable_count())),
       inlining_id_(-1) {
   DiscoverBlocks();
 }
 
 
 void FlowGraph::EnsureSSATempIndex(Definition* defn, Definition* replacement) {
   if ((replacement->ssa_temp_index() == -1) && (defn->ssa_temp_index() != -1)) {
     AllocateSSAIndexes(replacement);
   }
@@ skipping 2219 matching lines @@
                                                 Representation rep,
                                                 intptr_t cid) {
   ExtractNthOutputInstr* extract =
       new (Z) ExtractNthOutputInstr(new (Z) Value(instr), index, rep, cid);
   instr->ReplaceUsesWith(extract);
   InsertAfter(instr, extract, NULL, FlowGraph::kValue);
 }
 
 
 }  // namespace dart