Validation of `@protected` method invocations.

pkg/analyzer/lib/src/dart/element/element.dart

Index: pkg/analyzer/lib/src/dart/element/element.dart
diff --git a/pkg/analyzer/lib/src/dart/element/element.dart b/pkg/analyzer/lib/src/dart/element/element.dart
index 530539595434b8fb77939f46c74bcff8dd6329d4..7c321e65d952790de803d609c8133fce72a2cc2c 100644
--- a/pkg/analyzer/lib/src/dart/element/element.dart
+++ b/pkg/analyzer/lib/src/dart/element/element.dart
@@ -1562,12 +1562,23 @@ class ElementAnnotationImpl implements ElementAnnotation {
   static String _DEPRECATED_VARIABLE_NAME = "deprecated";
 
   /**
+   * The name of `meta` library, used to define analysis annotations.
+   */
+  static String _META_LIB_NAME = "meta";
+
+  /**
    * The name of the top-level variable used to mark a method as being expected
    * to override an inherited method.
    */
   static String _OVERRIDE_VARIABLE_NAME = "override";
 
   /**
+   * The name of the top-level variable used to mark a method as being
+   * protected.
+   */
+  static String _PROTECTED_VARIABLE_NAME = "protected";
+
+  /**
    * The name of the top-level variable used to mark a class as implementing a
    * proxy object.
    */
@@ -1644,6 +1655,20 @@ class ElementAnnotationImpl implements ElementAnnotation {
   }
 
   @override
+  bool get isProtected {
+    if (element != null) {
+      LibraryElement library = element.library;
+      if (library != null && library.name == _META_LIB_NAME) {
+        if (element is PropertyAccessorElement &&
+            element.name == _PROTECTED_VARIABLE_NAME) {
+          return true;
+        }
+      }
+    }
+    return false;
+  }
+
+  @override
   bool get isProxy {
     if (element != null) {
       LibraryElement library = element.library;
@@ -1837,6 +1862,16 @@ abstract class ElementImpl implements Element {
   }
 
   @override
+  bool get isProtected {
+    for (ElementAnnotation annotation in metadata) {
+      if (annotation.isProtected) {
+        return true;
+      }
+    }
+    return false;
+  }
+
+  @override
   bool get isPublic => !isPrivate;
 
   @override
@@ -3929,6 +3964,9 @@ class MultiplyDefinedElementImpl implements MultiplyDefinedElement {
   }
 
   @override
+  bool get isProtected => false;
+
+  @override
   bool get isPublic => !isPrivate;
 
   @override