Fix bug in container tracer, where a local would be updated with the wrong type in the expression `…

sdk/lib/_internal/compiler/implementation/inferrer/container_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 container_tracer;
 
 import '../dart2jslib.dart' hide Selector, TypedSelector;
 import '../elements/elements.dart';
 import '../tree/tree.dart';
 import '../universe/universe.dart';
@@ skipping 570 matching lines @@
         tracer.addEscapingElement(analyzedElement);
       } else if (element != null
                   && (!element.isInstanceMember() || visitingInitializers)) {
         // A local, a static element, or a field in an initializer.
         tracer.addEscapingElement(element);
       } else {
         tracer.addSettersToAnalysis(setterSelector);
       }
     }
 
-    if (Elements.isLocal(element)) {
-      locals.update(element, rhsType, node);
-    }
-
+    TypeMask result;
     if (node.isPostfix) {
       // We don't check if [getterSelector] could be the container because
       // a list++ will always throw.
-      return inferrer.returnTypeOfSelector(getterSelector);
+      result = inferrer.returnTypeOfSelector(getterSelector);
     } else if (op != '=') {
       // We don't check if [getterSelector] could be the container because
       // a list += 42 will always throw.
-      return inferrer.returnTypeOfSelector(operatorSelector);
+      result = inferrer.returnTypeOfSelector(operatorSelector);
     } else {
       if (isValueEscaping) {
         escaping = true;
       }
-      return rhsType;
+      result = rhsType;
     }
+
+    if (Elements.isLocal(element)) {
+      locals.update(element, result, node);
+    }
+
+    return result;
   }
 
   TypeMask visitSuperSend(Send node) {
     Element element = elements[node];
     if (!node.isPropertyAccess) {
       visitArguments(node.arguments, element);
     }
 
     if (tracer.couldBeTheList(element)) {
       escaping = true;
@@ skipping 176 matching lines @@
     Element element = elements[identifier];
     if (Elements.isLocal(element)) {
       locals.update(element, currentType, node);
     }
 
     return handleLoop(node, () {
       visit(node.body);
     });
   }
 }