Dart2js CPS: Implement 'await for'.

pkg/compiler/lib/src/tree_ir/optimization/pull_into_initializers.dart

 // Copyright (c) 2015, 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 tree_ir.optimization.pull_into_initializers;
 
 import 'optimization.dart' show Pass;
 import '../tree_ir_nodes.dart';
 
 /// Where a variable has been assigned.
@@ skipping 247 matching lines @@
     ++impureCounter;
     return node;
   }
 
   Expression visitOneShotInterceptor(OneShotInterceptor node) {
     super.visitOneShotInterceptor(node);
     ++impureCounter;
     return node;
   }
 
+  Expression visitAwait(Await node) {
+    super.visitAwait(node);
+    ++impureCounter;
+    return node;
+  }
+
   Expression visitConditional(Conditional node) {
     node.condition = visitExpression(node.condition);
     // Visit the branches to detect impure subexpressions, but do not pull
     // expressions out of the branch.
     ++branchCounter;
     node.thenExpression = visitExpression(node.thenExpression);
     node.elseExpression = visitExpression(node.elseExpression);
     --branchCounter;
     return node;
   }
@@ skipping 86 matching lines @@
 
   @override
   Expression visitForeignExpression(ForeignExpression node) {
     rewriteList(node.arguments);
     if (node.nativeBehavior.sideEffects.hasSideEffects()) {
       ++impureCounter;
     }
     return node;
   }
 }