Plumb "enableSuperMixins" option through analysis server (implements DEP 34).

pkg/analysis_server/lib/src/domain_analysis.dart

Index: pkg/analysis_server/lib/src/domain_analysis.dart
diff --git a/pkg/analysis_server/lib/src/domain_analysis.dart b/pkg/analysis_server/lib/src/domain_analysis.dart
index 483f5321b21c155f5e47d264b53d0de4a56488a3..c0492bf47cdd650559d3ab4d04bb246c6c4cd75c 100644
--- a/pkg/analysis_server/lib/src/domain_analysis.dart
+++ b/pkg/analysis_server/lib/src/domain_analysis.dart
@@ -281,6 +281,11 @@ class AnalysisDomainHandler implements RequestHandler {
         options.lint = newOptions.generateLints;
       });
     }
+    if (newOptions.enableSuperMixins != null) {
+      updaters.add((engine.AnalysisOptionsImpl options) {
+        options.enableSuperMixins = newOptions.enableSuperMixins;
+      });
+    }
     server.updateOptions(updaters);
     return new AnalysisUpdateOptionsResult().toResponse(request.id);
   }