Support optional function expression parameters in dart2js... and dart2dart.

sdk/lib/_internal/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.
 
 part of dart_backend;
 
 class LocalPlaceholder {
   final String identifier;
   final Set<Node> nodes;
   LocalPlaceholder(this.identifier) : nodes = new Set<Node>();
@@ skipping 405 matching lines @@
     } else if (!element.isErroneous()) {
       if (Elements.isStaticOrTopLevel(element)) {
         // TODO(smok): Worth investigating why sometimes we get getter/setter
         // here and sometimes abstract field.
         assert(element.isClass() || element is VariableElement ||
                element.isAccessor() || element.isAbstractField() ||
                element.isFunction() || element.isTypedef() ||
                element is TypeVariableElement);
         makeElementPlaceholder(send.selector, element);
       } else {
-        assert(send.selector is Identifier);
+        Identifier identifier = send.selector.asIdentifier();
+        if (identifier == null) {
+          // Handle optional function expression parameters with default values.
+          identifier = send.selector.asFunctionExpression().name;
+        }
         if (Elements.isInstanceField(element)) {
-          tryMakeMemberPlaceholder(send.selector);
+          tryMakeMemberPlaceholder(identifier);
         } else {
-          tryMakeLocalPlaceholder(element, send.selector);
+          tryMakeLocalPlaceholder(element, identifier);
         }
       }
     }
     send.visitChildren(this);
   }
 
   visitIdentifier(Identifier identifier) {
     if (identifier.source.isPrivate()) makePrivateIdentifier(identifier);
   }
 
@@ skipping 181 matching lines @@
 
   visitBlock(Block node) {
     for (Node statement in node.statements.nodes) {
       if (statement is VariableDefinitions) {
         makeVarDeclarationTypePlaceholder(statement);
       }
     }
     node.visitChildren(this);
   }
 }