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

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

Index: pkg/analyzer/lib/src/generated/resolver.dart
diff --git a/pkg/analyzer/lib/src/generated/resolver.dart b/pkg/analyzer/lib/src/generated/resolver.dart
index 474642ae4338266461ab1140774d7ff043a4056b..958c65e8782cdba5b5f8a7480f3c7fd110025707 100644
--- a/pkg/analyzer/lib/src/generated/resolver.dart
+++ b/pkg/analyzer/lib/src/generated/resolver.dart
@@ -753,8 +753,13 @@ class BestPracticesVerifier extends RecursiveAstVisitor<Object> {
         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);