Add the 'docRange' property and use it to compute documentation comment.

pkg/analyzer/lib/src/generated/testing/ast_factory.dart

Index: pkg/analyzer/lib/src/generated/testing/ast_factory.dart
diff --git a/pkg/analyzer/lib/src/generated/testing/ast_factory.dart b/pkg/analyzer/lib/src/generated/testing/ast_factory.dart
index 86f1e049ba364d67706b6b12b65861cc92a4a311..bb758b3533f72dcd7bf850f6430e114dc7ad8e7e 100644
--- a/pkg/analyzer/lib/src/generated/testing/ast_factory.dart
+++ b/pkg/analyzer/lib/src/generated/testing/ast_factory.dart
@@ -377,6 +377,11 @@ class AstFactory {
           TypeName type, String identifier) =>
       declaredIdentifier2(null, type, identifier);
 
+  static Comment documentationComment(
+      List<Token> tokens, List<CommentReference> references) {
+    return new Comment(tokens, CommentType.DOCUMENTATION, references);
+  }
+
   static DoStatement doStatement(Statement body, Expression condition) =>
       new DoStatement(
           TokenFactory.tokenFromKeyword(Keyword.DO),