Fix a couple of bugs with async stack traces

runtime/vm/code_generator.cc

 // Copyright (c) 2013, 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/code_generator.h"
 
 #include "vm/assembler.h"
 #include "vm/ast.h"
 #include "vm/code_patcher.h"
 #include "vm/compiler.h"
@@ skipping 1613 matching lines @@
       frame->function().EnsureHasCompiledUnoptimizedCode();
 #endif
       // Variable locations and number are unknown when precompiling.
       const int num_vars =
           FLAG_precompiled_runtime ? 0 : frame->NumLocalVariables();
       TokenPosition unused = TokenPosition::kNoSource;
       for (intptr_t v = 0; v < num_vars; v++) {
         frame->VariableAt(v, &var_name, &unused, &unused, &unused, &var_value);
       }
     }
+    if (FLAG_stress_async_stacks) {
+      Debugger::CollectAwaiterReturnStackTrace();
+    }
     FLAG_stacktrace_every = saved_stacktrace_every;
   }
 
   const Error& error = Error::Handle(thread->HandleInterrupts());
   if (!error.IsNull()) {
     Exceptions::PropagateError(error);
     UNREACHABLE();
   }
 
   if ((stack_overflow_flags & Thread::kOsrRequest) != 0) {
@@ skipping 572 matching lines @@
   const intptr_t elm_size = old_data.ElementSizeInBytes();
   const TypedData& new_data =
       TypedData::Handle(TypedData::New(cid, new_size, Heap::kOld));
   TypedData::Copy(new_data, 0, old_data, 0, old_size * elm_size);
   typed_data_cell.SetAt(0, new_data);
   arguments.SetReturn(new_data);
 }
 
 
 }  // namespace dart