Handle SendSet and NewExpression through NewResolvedVisitor.

pkg/compiler/lib/src/dart_backend/placeholder_collector.dart

Index: pkg/compiler/lib/src/dart_backend/placeholder_collector.dart
diff --git a/pkg/compiler/lib/src/dart_backend/placeholder_collector.dart b/pkg/compiler/lib/src/dart_backend/placeholder_collector.dart
index 4d47c149e2c7e47562c5a69bf5a003266288fe7e..f8b5495df509510c8b2d838231db41d7f93149d4 100644
--- a/pkg/compiler/lib/src/dart_backend/placeholder_collector.dart
+++ b/pkg/compiler/lib/src/dart_backend/placeholder_collector.dart
@@ -152,6 +152,12 @@ class SendVisitor extends OldResolvedVisitor {
       }
     }
   }
+
+  @override
+  handleNewExpression(NewExpression node) => visitNode(node);
+
+  @override
+  handleSendSet(SendSet node) => visitNode(node);
 }
 
 class PlaceholderCollector extends Visitor {