[dart2dart] Fix assertions for tests to pass in checked mode.

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 {
   final String identifier;
   final Set<Node> nodes;
   LocalPlaceholder(this.identifier) : nodes = new Set<Node>();
   int hashCode() => identifier.hashCode();
   String toString() =>
@@ skipping 376 matching lines @@
       // Complicated case: constructs like receiver.selector++ can resolve
       // to ErroneousElement.  Fortunately, receiver.selector still
       // can be resoved via treeElements[send.selector], that's all
       // that is needed to rename the construct properly.
       element = treeElements[send.selector];
     }
     if (element === null) {
       if (send.receiver !== null) tryMakeMemberPlaceholder(send.selector);
     } else if (!element.isErroneous()) {
       if (Elements.isStaticOrTopLevel(element)) {
-        assert(element is VariableElement || element.isAccessor());
+        // TODO(smok): Worth investigating why sometimes we get getter/setter
+        // here and sometimes abstract field.
+        assert(element is VariableElement || element.isAccessor()
+            || element.isAbstractField() || element.isFunction());
         makeElementPlaceholder(send.selector, element);
       } else {
         assert(send.selector is Identifier);
         if (Elements.isInstanceField(element)) {
           tryMakeMemberPlaceholder(send.selector);
         } else {
           tryMakeLocalPlaceholder(element, send.selector);
         }
       }
     }
@@ skipping 224 matching lines @@
 
   visitBlock(Block node) {
     for (Node statement in node.statements.nodes) {
       if (statement is VariableDefinitions) {
         makeVarDeclarationTypePlaceholder(statement);
       }
     }
     node.visitChildren(this);
   }
 }