Enable causal stacktrace in kernel

pkg/kernel/lib/transformations/continuation.dart

 // Copyright (c) 2016, 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.
 
 library kernel.transformations.continuation;
 
 import 'dart:math' as math;
 
 import '../ast.dart';
 import '../core_types.dart';
@@ skipping 180 matching lines @@
   }
 }
 
 abstract class AsyncRewriterBase extends ContinuationRewriterBase {
   final VariableDeclaration nestedClosureVariable =
       new VariableDeclaration(":async_op");
   final VariableDeclaration thenContinuationVariable =
       new VariableDeclaration(":async_op_then");
   final VariableDeclaration catchErrorContinuationVariable =
       new VariableDeclaration(":async_op_error");
+  final VariableDeclaration asyncStackTrace =
+      new VariableDeclaration(":async_stack_trace");
 
   LabeledStatement labeledBody;
 
   ExpressionLifter expressionRewriter;
 
   AsyncRewriterBase(helper, enclosingFunction)
       : super(helper, enclosingFunction) {}
 
   void setupAsyncContinuations(List<Statement> statements) {
     expressionRewriter = new ExpressionLifter(this);
 
     // var :async_op_then;
     statements.add(thenContinuationVariable);
 
     // var :async_op_error;
     statements.add(catchErrorContinuationVariable);
 
+    // var :async_stack_trace;
+    statements.add(asyncStackTrace);
+
     // :async_op([:result, :exception, :stack_trace]) {
     //     modified <node.body>;
     // }
     final parameters = <VariableDeclaration>[
       expressionRewriter.asyncResult,
       new VariableDeclaration(':exception'),
       new VariableDeclaration(':stack_trace'),
     ];
     final function = new FunctionNode(buildWrappedBody(),
         positionalParameters: parameters,
@@ skipping 741 matching lines @@
         findConstructor(syncIterableClass, ''),
         findConstructor(streamIteratorClass, ''),
         findFactoryConstructor(futureClass, 'microtask'),
         findConstructor(streamControllerClass, ''),
         findProcedure(asyncLibrary, '_asyncThenWrapperHelper'),
         findProcedure(asyncLibrary, '_asyncErrorWrapperHelper'),
         findProcedure(asyncLibrary, '_awaitHelper'),
         new CoreTypes(program));
   }
 }