Warn on private members.

sdk/lib/_internal/compiler/implementation/warnings.dart

 // Copyright (c) 2011, 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 dart2js;
 
 class MessageKind {
   final String template;
   const MessageKind(this.template);
 
@@ skipping 20 matching lines @@
   static const OPERATOR_NOT_FOUND = const MessageKind(
       'no operator #{memberName} in class #{className}');
   static const PROPERTY_NOT_FOUND = const MessageKind(
       'no property named #{memberName} in class #{className}');
   static const NOT_CALLABLE = const MessageKind(
       "'#{elementName}' is not callable");
   static const MEMBER_NOT_STATIC = const MessageKind(
       '#{className}.#{memberName} is not static');
   static const NO_INSTANCE_AVAILABLE = const MessageKind(
       '#{name} is only available in instance methods');
+  static const PRIVATE_ACCESS = const MessageKind(
+      "'#{name}' is declared private within library #{libraryName} and "
+      "is therefore not accessible.");
 
   static const THIS_IS_THE_METHOD = const MessageKind(
       "This is the method declaration.");
 
   static const UNREACHABLE_CODE = const MessageKind(
       'unreachable code');
   static const MISSING_RETURN = const MessageKind(
       'missing return');
   static const MAYBE_MISSING_RETURN = const MessageKind(
       'not all paths lead to a return or throw statement');
@@ skipping 562 matching lines @@
 
 class CompileTimeConstantError extends Diagnostic {
   CompileTimeConstantError(MessageKind kind, [Map arguments = const {}])
     : super(kind, arguments);
 }
 
 class CompilationError extends Diagnostic {
   CompilationError(MessageKind kind, [Map arguments = const {}])
     : super(kind, arguments);
 }