Fix serialization of IndexSetIfNullStructure.

pkg/compiler/lib/src/resolution/send_structure.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 dart2js.resolution.send_structure;
 
 import '../common.dart';
 import '../constants/expressions.dart';
 import '../dart_types.dart';
 import '../elements/elements.dart';
@@ skipping 1486 matching lines @@
 
 /// The structure for a [Send] that is a if-null assignment on the index
 /// operator. For instance `a[b] ??= c`.
 class IndexSetIfNullStructure<R, A> implements SendStructure<R, A> {
   /// The target of the index operations.
   final AccessSemantics semantics;
 
   IndexSetIfNullStructure(this.semantics);
 
   @override
-  SendStructureKind get kind => SendStructureKind.INDEX_SET;
+  SendStructureKind get kind => SendStructureKind.INDEX_SET_IF_NULL;
 
   R dispatch(SemanticSendVisitor<R, A> visitor, Send node, A arg) {
     switch (semantics.kind) {
       case AccessKind.EXPRESSION:
         return visitor.visitIndexSetIfNull(node, node.receiver,
             node.arguments.first, node.arguments.tail.head, arg);
       case AccessKind.UNRESOLVED_SUPER:
         return visitor.visitUnresolvedSuperIndexSetIfNull(
             node,
             semantics.element,
@@ skipping 992 matching lines @@
   ThisConstructorInvokeStructure(
       this.node, this.constructor, this.callStructure);
 
   R dispatch(SemanticDeclarationVisitor<R, A> visitor, A arg) {
     return visitor.visitThisConstructorInvoke(
         node, constructor, node.argumentsNode, callStructure, arg);
   }
 
   bool get isConstructorInvoke => true;
 }