Fix another missing source location VM stacktrace with async code.

runtime/vm/ast_transformer.cc

 // Copyright (c) 2014, 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/ast_transformer.h"
 
 #include "vm/object_store.h"
 #include "vm/parser.h"
 #include "vm/thread.h"
 
@@ skipping 168 matching lines @@
 
   AwaitMarkerNode* await_marker = new (Z) AwaitMarkerNode();
   await_marker->set_scope(preamble_->scope());
   preamble_->Add(await_marker);
   ArgumentListNode* args = new(Z) ArgumentListNode(Scanner::kNoSourcePos);
 
   args->Add(new(Z) LoadLocalNode(Scanner::kNoSourcePos, async_op));
   preamble_->Add(new (Z) StoreLocalNode(
       Scanner::kNoSourcePos,
       result_param,
-      new(Z) InstanceCallNode(Scanner::kNoSourcePos,
+      new(Z) InstanceCallNode(node->token_pos(),
                               load_result_param,
                               Symbols::FutureThen(),
                               args)));
   const Library& core_lib = Library::Handle(Library::CoreLibrary());
   const Function& async_catch_helper = Function::ZoneHandle(
       Z, core_lib.LookupFunctionAllowPrivate(Symbols::AsyncCatchHelper()));
   ASSERT(!async_catch_helper.IsNull());
   ArgumentListNode* catch_helper_args = new (Z) ArgumentListNode(
       Scanner::kNoSourcePos);
   InstanceGetterNode* catch_error_getter = new (Z) InstanceGetterNode(
@@ skipping 399 matching lines @@
 void AwaitTransformer::VisitThrowNode(ThrowNode* node) {
   // TODO(mlippautz): Check if relevant.
   AstNode* new_exception = Transform(node->exception());
   AstNode* new_stacktrace = Transform(node->stacktrace());
   result_ = new(Z) ThrowNode(node->token_pos(),
                              new_exception,
                              new_stacktrace);
 }
 
 }  // namespace dart