Emit read-modify-write of fields as assignment op.

sdk/lib/_internal/compiler/implementation/ssa/tracer.dart

 // Copyright (c) 2013, 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 tracer;
 
 import 'dart:async' show EventSink;
 
 import 'ssa.dart';
 import '../js_backend/js_backend.dart';
@@ skipping 257 matching lines @@
     String fieldName = node.element.name;
     return 'field get ${temporaryId(node.receiver)}.$fieldName';
   }
 
   String visitFieldSet(HFieldSet node) {
     String valueId = temporaryId(node.value);
     String fieldName = node.element.name;
     return 'field set ${temporaryId(node.receiver)}.$fieldName to $valueId';
   }
 
+  String visitReadModifyWrite(HReadModifyWrite node) {
+    String fieldName = node.element.name;
+    String receiverId = temporaryId(node.receiver);
+    String op = node.jsOp;
+    if (node.isAssignOp) {
+      String valueId = temporaryId(node.value);
+      return 'field-update $receiverId.$fieldName $op= $valueId';
+    } else if (node.isPreOp) {
+      return 'field-update $op$receiverId.$fieldName';
+    } else {
+      return 'field-update $receiverId.$fieldName$op';
+    }
+  }
+
   String visitLocalGet(HLocalGet node) {
     String localName = node.element.name;
     return 'local get ${temporaryId(node.local)}.$localName';
   }
 
   String visitLocalSet(HLocalSet node) {
     String valueId = temporaryId(node.value);
     String localName = node.element.name;
     return 'local set ${temporaryId(node.local)}.$localName to $valueId';
   }
@@ skipping 261 matching lines @@
   }
 
   String visitInterfaceType(HInterfaceType node) {
     return "InterfaceType: ${node.dartType}";
   }
 
   String visitDynamicType(HDynamicType node) {
     return "DynamicType";
   }
 }