Ensure libraries always have at least one top-level class and therefore at least one script.

runtime/vm/parser.cc

 // 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.
 
 #include "vm/parser.h"
 
 #include "lib/invocation_mirror.h"
 #include "platform/utils.h"
 #include "vm/ast_transformer.h"
 #include "vm/bootstrap.h"
@@ skipping 5952 matching lines @@
         ParseTopLevelFunction(&top_level, metadata_pos);
       } else if (IsTopLevelAccessor()) {
         ParseTopLevelAccessor(&top_level, metadata_pos);
       } else if (CurrentToken() == Token::kEOS) {
         break;
       } else {
         UnexpectedToken();
       }
     }
   }
-  if ((top_level.fields.Length() > 0) || (top_level.functions.Length() > 0)) {
+
+  if ((library_.num_anonymous_classes() == 0) ||
+    (top_level.fields.Length() > 0) || (top_level.functions.Length() > 0)) {
     toplevel_class.AddFields(top_level.fields);
 
     const Array& array = Array::Handle(Z,
                                        Array::MakeArray(top_level.functions));
     toplevel_class.SetFunctions(array);
 
     library_.AddAnonymousClass(toplevel_class);
     pending_classes.Add(toplevel_class, Heap::kOld);
   }
 }
@@ skipping 7491 matching lines @@
 void Parser::SkipQualIdent() {
   ASSERT(IsIdentifier());
   ConsumeToken();
   if (CurrentToken() == Token::kPERIOD) {
     ConsumeToken();  // Consume the kPERIOD token.
     ExpectIdentifier("identifier expected after '.'");
   }
 }
 
 }  // namespace dart