Just ignore erroneous elements.

lib/compiler/implementation/dart_backend/placeholder_collector.dart

Index: lib/compiler/implementation/dart_backend/placeholder_collector.dart
diff --git a/lib/compiler/implementation/dart_backend/placeholder_collector.dart b/lib/compiler/implementation/dart_backend/placeholder_collector.dart
index 1f697c8f190f493d071f1a5eb378e4ca304d6272..14a2674167a5b74b88b90235c2352e09b1cd4951 100644
--- a/lib/compiler/implementation/dart_backend/placeholder_collector.dart
+++ b/lib/compiler/implementation/dart_backend/placeholder_collector.dart
@@ -28,6 +28,8 @@ class SendVisitor extends ResolvedVisitor {
   }
 
   visitDynamicSend(Send node) {
+    Element element = elements[node];
+    if (element !== null && element.isErroneous()) return;
     tryRenamePrivateSelector(node);
   }
 
@@ -314,13 +316,6 @@ class PlaceholderCollector extends AbstractVisitor {
   visitNode(Node node) { node.visitChildren(this); }  // We must go deeper.
 
   visitSend(Send send) {
-    Element element = treeElements[send];
-    if (element !== null && element.isErroneous()) {
-      // TODO(antonm): this is an unresolved constructor, not a dynamic send.
-      ErroneousElement erroneousElement = element;
-      compiler.cancel(reason: erroneousElement.errorMessage.toString(),
-                      node: send);
-    }
     new SendVisitor(this, treeElements).visitSend(send);
     send.visitChildren(this);
   }