Fix an issue with restoring certain lint issues from summary files.

pkg/analyzer/lib/src/lint/registry.dart

Index: pkg/analyzer/lib/src/lint/registry.dart
diff --git a/pkg/analyzer/lib/src/lint/registry.dart b/pkg/analyzer/lib/src/lint/registry.dart
index 172767ba598e2f68d70fb65bc8c080cfab55045b..241108baf384df689d3a45ea74d253b75fcfc5c6 100644
--- a/pkg/analyzer/lib/src/lint/registry.dart
+++ b/pkg/analyzer/lib/src/lint/registry.dart
@@ -45,6 +45,11 @@ class Registry extends Object with IterableMixin<LintRule> {
   LintRule operator [](String name) => _ruleMap[name];
 
   /**
+   * Return the lint rule with the given [name].
+   */
+  LintRule getRule(String name) => _ruleMap[name];
+
+  /**
    * Return a list of the lint rules explicitly enabled by the given [config].
    *
    * For example: