dart2js cps: Support async/await by rewriting the JavaScript AST.

pkg/compiler/lib/src/cps_ir/shrinking_reductions.dart

 // 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.
 
 library dart2js.cps_ir.shrinking_reductions;
 
 import 'cps_ir_nodes.dart';
 import 'optimizers.dart';
 
 /**
@@ skipping 669 matching lines @@
   processGetIndex(GetIndex node) {
     node.object.parent = node;
     node.index.parent = node;
   }
 
   processSetIndex(SetIndex node) {
     node.object.parent = node;
     node.index.parent = node;
     node.value.parent = node;
   }
+
+  processAwait(Await node) {
+    node.continuation.parent = node;
+    node.input.parent = node;
+  }
 }
 
 class _ReductionKind {
   final String name;
   final int hashCode;
 
   const _ReductionKind(this.name, this.hashCode);
 
   static const _ReductionKind DEAD_VAL = const _ReductionKind('dead-val', 0);
   static const _ReductionKind DEAD_CONT = const _ReductionKind('dead-cont', 1);
@@ skipping 26 matching lines @@
   }
 
   String toString() => "$kind: $node";
 }
 
 /// A dummy class used solely to mark nodes as deleted once they are removed
 /// from a term.
 class _DeletedNode extends Node {
   accept(_) => null;
 }