Analyzer support for `@factory` methods (linter#253).

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

Index: pkg/analyzer/lib/dart/element/element.dart
diff --git a/pkg/analyzer/lib/dart/element/element.dart b/pkg/analyzer/lib/dart/element/element.dart
index 13fbe4800383ea78306cb74c470e0bf73ba3718e..b829beed070b230382d275e103e98208b085ea62 100644
--- a/pkg/analyzer/lib/dart/element/element.dart
+++ b/pkg/analyzer/lib/dart/element/element.dart
@@ -624,6 +624,11 @@ abstract class Element implements AnalysisTarget {
   bool get isDeprecated;
 
   /**
+   * Return `true` if this element has an annotation of the form '@factory'.
+   */
+  bool get isFactory;
+
+  /**
    * Return `true` if this element has an annotation of the form '@JS(..)'.
    */
   bool get isJS;
@@ -819,6 +824,11 @@ abstract class ElementAnnotation implements ConstantEvaluationTarget {
   bool get isDeprecated;
 
   /**
+   * Return `true` if this annotation marks the associated member as a factory.
+   */
+  bool get isFactory;
+
+  /**
    * Return `true` if this annotation marks the associated element with the `JS`
    * annotation.
    */