Fix test failures on the bots

pkg/analysis_server/test/analysis_abstract.dart

Index: pkg/analysis_server/test/analysis_abstract.dart
diff --git a/pkg/analysis_server/test/analysis_abstract.dart b/pkg/analysis_server/test/analysis_abstract.dart
index 7af9a462a8d86ff25325bad441b007aaad41069e..2406a06224dbf24aa1beefc8ec4a8287ee1e2834 100644
--- a/pkg/analysis_server/test/analysis_abstract.dart
+++ b/pkg/analysis_server/test/analysis_abstract.dart
@@ -191,6 +191,11 @@ class AbstractAnalysisTest {
   }
 
   void setUp() {
+    ExtensionManager manager = new ExtensionManager();
+    ServerPlugin serverPlugin = new ServerPlugin();
+    List<Plugin> plugins = [serverPlugin];
+    plugins.addAll(AnalysisEngine.instance.supportedPlugins);
+    manager.processPlugins(plugins);
     serverChannel = new MockServerChannel();
     resourceProvider = new MemoryResourceProvider();
     packageMapProvider = new MockPackageMapProvider();