Revert "Clean-up the registration of plugins"

pkg/analyzer_cli/lib/src/driver.dart

Index: pkg/analyzer_cli/lib/src/driver.dart
diff --git a/pkg/analyzer_cli/lib/src/driver.dart b/pkg/analyzer_cli/lib/src/driver.dart
index 037036890664b5cb85f3afd2d5c1d82c2a04cfd8..752cb1e87597f572754ca4169c4936a35a1a6f7d 100644
--- a/pkg/analyzer_cli/lib/src/driver.dart
+++ b/pkg/analyzer_cli/lib/src/driver.dart
@@ -35,7 +35,6 @@ import 'package:package_config/packages.dart' show Packages;
 import 'package:package_config/packages_file.dart' as pkgfile show parse;
 import 'package:package_config/src/packages_impl.dart' show MapPackages;
 import 'package:path/path.dart' as path;
-import 'package:plugin/manager.dart';
 import 'package:plugin/plugin.dart';
 import 'package:yaml/yaml.dart';
 
@@ -501,12 +500,12 @@ class Driver {
 
   void _processPlugins() {
     List<Plugin> plugins = <Plugin>[];
-    plugins.addAll(AnalysisEngine.instance.supportedPlugins);
     plugins.add(linterPlugin);
     plugins.addAll(_userDefinedPlugins);
+    AnalysisEngine.instance.userDefinedPlugins = plugins;
 
-    ExtensionManager manager = new ExtensionManager();
-    manager.processPlugins(plugins);
+    // This ensures that AE extension manager processes plugins.
+    AnalysisEngine.instance.taskManager;
   }
 
   /// Analyze a single source.