Revert "Clean-up the registration of plugins"

pkg/analyzer/lib/src/generated/engine.dart

Index: pkg/analyzer/lib/src/generated/engine.dart
diff --git a/pkg/analyzer/lib/src/generated/engine.dart b/pkg/analyzer/lib/src/generated/engine.dart
index ac626cc4cbba289bb06027e19913e4dacc754f57..597d3819955bd14e5fb190d9804c795455079bfc 100644
--- a/pkg/analyzer/lib/src/generated/engine.dart
+++ b/pkg/analyzer/lib/src/generated/engine.dart
@@ -5925,6 +5925,11 @@ class AnalysisEngine {
       InstrumentationService.NULL_SERVICE;
 
   /**
+   * The list of supported plugins for processing by clients.
+   */
+  List<Plugin> _supportedPlugins;
+
+  /**
    * The partition manager being used to manage the shared partitions.
    */
   final PartitionManager partitionManager = new PartitionManager();
@@ -5948,6 +5953,11 @@ class AnalysisEngine {
   bool limitInvalidationInTaskModel = false;
 
   /**
+   * The plugins that are defined outside the `analyzer` package.
+   */
+  List<Plugin> _userDefinedPlugins = <Plugin>[];
+
+  /**
    * The task manager used to manage the tasks used to analyze code.
    */
   TaskManager _taskManager;
@@ -5989,18 +5999,24 @@ class AnalysisEngine {
   /**
    * Return the list of supported plugins for processing by clients.
    */
-  List<Plugin> get supportedPlugins =>
-      <Plugin>[enginePlugin, commandLinePlugin, optionsPlugin];
+  List<Plugin> get supportedPlugins {
+    if (_supportedPlugins == null) {
+      _supportedPlugins = <Plugin>[
+        enginePlugin,
+        commandLinePlugin,
+        optionsPlugin
+      ];
+      _supportedPlugins.addAll(_userDefinedPlugins);
+    }
+    return _supportedPlugins;
+  }
 
   /**
    * Return the task manager used to manage the tasks used to analyze code.
    */
   TaskManager get taskManager {
     if (_taskManager == null) {
-      if (enginePlugin.taskExtensionPoint == null) {
-        throw new IllegalStateException(
-            'The analysis engine plugin has not been registered');
-      }
+      new ExtensionManager().processPlugins(supportedPlugins);
       _taskManager = new TaskManager();
       _taskManager.addTaskDescriptors(enginePlugin.taskDescriptors);
       // TODO(brianwilkerson) Create a way to associate different results with
@@ -6011,6 +6027,18 @@ class AnalysisEngine {
   }
 
   /**
+   * Set plugins that are defined outside the `analyzer` package.
+   */
+  void set userDefinedPlugins(List<Plugin> plugins) {
+    if (plugins == null) {
+      plugins = <Plugin>[];
+    }
+    _userDefinedPlugins = plugins;
+    _supportedPlugins = null;
+    _taskManager = null;
+  }
+
+  /**
    * Clear any caches holding on to analysis results so that a full re-analysis
    * will be performed the next time an analysis context is created.
    */
@@ -9423,7 +9451,7 @@ abstract class InternalAnalysisContext implements AnalysisContext {
 
   /// Get the [EmbedderYamlLocator] for this context.
   EmbedderYamlLocator get embedderYamlLocator;
-
+  
   /**
    * A factory to override how [ResolverVisitor] is created.
    */