dart2dart Fix setter ref with library prefix.

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 22 matching lines @@
 
   visitGetterSend(Send node) {
     final element = elements[node];
     // element === null means dynamic property access.
     if (element === null || element.isInstanceMember()) {
       tryRenamePrivateSelector(node);
       return;
     }
     // We don't want to rename non top-level element access
     // unless it's a local variable.
-    if (!element.isTopLevel()) {
+    if (element.isPrefix()) {
+      // Node is prefix part in case of source 'lib.somesetter = 5;'
+      collector.makeNullPlaceholder(node);
+      return;
+    } else if (!element.isTopLevel()) {
       // May get FunctionExpression here in selector
       // in case of A(int this.f());
       if (node.selector is Identifier) {
         collector.tryMakeLocalPlaceholder(element, node.selector);
       } else {
         assert(node.selector is FunctionExpression);
       }
       return;
     }
     // Unqualified <class> in static invocation, why it's not a type annotation?
@@ skipping 362 matching lines @@
     makeElementPlaceholder(node.name, currentElement);
     node.visitChildren(this);
   }
 
   visitTypedef(Typedef node) {
     assert(currentElement is TypedefElement);
     makeElementPlaceholder(node.name, currentElement);
     node.visitChildren(this);
   }
 }