Clean up wording of client usage expectations

pkg/analysis_server/lib/plugin/analysis/analysis_domain.dart

Index: pkg/analysis_server/lib/plugin/analysis/analysis_domain.dart
diff --git a/pkg/analysis_server/lib/plugin/analysis/analysis_domain.dart b/pkg/analysis_server/lib/plugin/analysis/analysis_domain.dart
index feca11aedbe51d4a7cda035488b63529f6e9d57d..821a81e1769b7a5c5067f5649c8ff34d3d6ce468 100644
--- a/pkg/analysis_server/lib/plugin/analysis/analysis_domain.dart
+++ b/pkg/analysis_server/lib/plugin/analysis/analysis_domain.dart
@@ -57,7 +57,7 @@ typedef void SetAnalysisDomain(AnalysisDomain domain);
  * An object that gives plugins access to the analysis domain of the analysis
  * server.
  *
- * Clients are not expected to subtype this class.
+ * Clients may not extend, implement or mix-in this class.
  */
 abstract class AnalysisDomain {
   /**