Fix test failures on the bots

pkg/analysis_server/test/abstract_context.dart

Index: pkg/analysis_server/test/abstract_context.dart
diff --git a/pkg/analysis_server/test/abstract_context.dart b/pkg/analysis_server/test/abstract_context.dart
index 46f0dbf2a027bd5a94111d50925e2e9c2f4aea90..e5b375cf920a4bb27d446093babdbf0b3d83cb62 100644
--- a/pkg/analysis_server/test/abstract_context.dart
+++ b/pkg/analysis_server/test/abstract_context.dart
@@ -12,6 +12,7 @@ import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/sdk.dart';
 import 'package:analyzer/src/generated/source_io.dart';
+import 'package:plugin/manager.dart';
 
 import 'mock_sdk.dart';
 
@@ -83,6 +84,8 @@ class AbstractContextTest {
   }
 
   void setUp() {
+    ExtensionManager extensionManager = new ExtensionManager();
+    extensionManager.processPlugins(AnalysisEngine.instance.supportedPlugins);
     setupResourceProvider();
     resourceResolver = new ResourceUriResolver(provider);
     packageMap = new Map<String, List<Folder>>();