Just ignore erroneous elements.

lib/compiler/implementation/dart_backend/placeholder_collector.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.
 
 class LocalPlaceholder implements Hashable {
   final String identifier;
   final Set<Node> nodes;
   LocalPlaceholder(this.identifier) : nodes = new Set<Node>();
   int hashCode() => identifier.hashCode();
   String toString() =>
@@ skipping 10 matching lines @@
   visitForeignSend(Send node) {}
 
   visitClosureSend(Send node) {
     final element = elements[node];
     if (element !== null) {
       collector.tryMakeLocalPlaceholder(element, node.selector);
     }
   }
 
   visitDynamicSend(Send node) {
+    Element element = elements[node];
+    if (element !== null && element.isErroneous()) return;
     tryRenamePrivateSelector(node);
   }
 
   visitGetterSend(Send node) {
     final element = elements[node];
     // element === null means dynamic property access.
     if (element === null || element.isMember()) {
       tryRenamePrivateSelector(node);
       return;
     }
@@ skipping 266 matching lines @@
     compiler.cancel(reason: reason, node: node);
   }
 
   void unreachable() { internalError('Unreachable case'); }
 
   visit(Node node) => (node === null) ? null : node.accept(this);
 
   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);
   }
 
   visitSendSet(SendSet send) {
     if (send.selector is Identifier) {
       tryMakePrivateIdentifier(send.selector.asIdentifier());
     }
     final element = treeElements[send];
     if (element !== null) {
@@ skipping 132 matching lines @@
       visit(node.defaultClause.typeArguments);
     }
   }
 
   visitTypedef(Typedef node) {
     assert(currentElement is TypedefElement);
     makeElementPlaceholder(node.name, currentElement);
     node.visitChildren(this);
   }
 }