Allow for library access to `@protected` protected members (linter#254).

pkg/analyzer/lib/src/generated/resolver.dart

 // Copyright (c) 2014, 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.
 
 library analyzer.src.generated.resolver;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
@@ skipping 735 matching lines @@
           element.isProtected) {
         return true;
       }
       return false;
     }
 
     bool inCommentReference(SimpleIdentifier identifier) =>
         identifier.getAncestor((AstNode node) => node is CommentReference) !=
         null;
 
+    bool inCurrentLibrary(Element element) =>
+        element.library == _currentLibrary;
+
     Element element = identifier.bestElement;
-    if (isProtected(element) && !inCommentReference(identifier)) {
+    if (isProtected(element) &&
+        !inCurrentLibrary(element) &&
+        !inCommentReference(identifier)) {
       ClassElement definingClass = element.enclosingElement;
       ClassDeclaration accessingClass =
           identifier.getAncestor((AstNode node) => node is ClassDeclaration);
       if (accessingClass == null ||
           !_hasTypeOrSuperType(accessingClass.element, definingClass.type)) {
         _errorReporter.reportErrorForNode(
             HintCode.INVALID_USE_OF_PROTECTED_MEMBER,
             identifier,
             [identifier.name.toString(), definingClass.name]);
       }
@@ skipping 10250 matching lines @@
       return null;
     }
     if (identical(node.staticElement, variable)) {
       if (node.inSetterContext()) {
         result = true;
       }
     }
     return null;
   }
 }