Resolve op when op= syntax is used.

lib/compiler/implementation/resolver.dart

 // Copyright (c) 2012, 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.
 
 abstract class TreeElements {
   Element operator[](Node node);
   Selector getSelector(Send send);
   DartType getType(TypeAnnotation annotation);
   bool isParameterChecked(Element element);
 }
@@ skipping 1482 matching lines @@
     // unqualified.
     useElement(node, target);
     registerSend(selector, target);
     return node.isPropertyAccess ? target : null;
   }
 
   visitSendSet(SendSet node) {
     Element target = resolveSend(node);
     Element setter = target;
     Element getter = target;
-    String source = node.assignmentOperator.source.stringValue;
+    SourceString operatorName = node.assignmentOperator.source;
+    String source = operatorName.stringValue;
     bool isComplex = source !== '=';
     if (!Elements.isUnresolved(target)
         && target.kind == ElementKind.ABSTRACT_FIELD) {
       AbstractFieldElement field = target;
       setter = field.setter;
       getter = field.getter;
       if (setter == null && !inInstanceContext) {
         setter =
             warnAndCreateErroneousElement(node.selector, field.name,
                                           MessageKind.CANNOT_RESOLVE_SETTER,
@@ skipping 28 matching lines @@
         // TODO(kasperl): If [getter] is resolved, it will actually
         // refer to the []= operator which isn't the one we want to
         // register here. We should consider using some notion of
         // abstract indexable element that we can resolve to so we can
         // distinguish the two.
         assert(selector.isIndexSet());
         registerSend(new Selector.index(), null);
       }
 
       // Make sure we include the + and - operators if we are using
-      // the ++ and -- ones.
+      // the ++ and -- ones.  Also, if op= form is used, include op itself.
       void registerBinaryOperator(SourceString name) {
         Selector binop = new Selector.binaryOperator(name);
         world.registerDynamicInvocation(binop.name, binop);
       }
       if (source === '++') registerBinaryOperator(const SourceString('+'));
       if (source === '--') registerBinaryOperator(const SourceString('-'));
+      if (source.endsWith('=')) {
+        registerBinaryOperator(Elements.mapToUserOperator(operatorName));
+      }
     }
 
     registerSend(selector, setter);
     return useElement(node, setter);
   }
 
   void registerSend(Selector selector, Element target) {
     if (target === null || target.isInstanceMember()) {
       if (selector.isGetter()) {
         world.registerDynamicGetter(selector.name, selector);
@@ skipping 1302 matching lines @@
 
   Element localLookup(SourceString name) => library.find(name);
   Element lookup(SourceString name) => localLookup(name);
   Element lexicalLookup(SourceString name) => localLookup(name);
 
   Element add(Element newElement) {
     throw "Cannot add an element in the top scope";
   }
   String toString() => '$element';
 }