Add DartWorkManager to manage Dart-specific results computation scheduling.

pkg/analyzer/lib/src/task/driver.dart

Index: pkg/analyzer/lib/src/task/driver.dart
diff --git a/pkg/analyzer/lib/src/task/driver.dart b/pkg/analyzer/lib/src/task/driver.dart
index 4abd9b3fe8ab84c99cc850dfcea192b8a10d861f..17149227675dfbc60c8db9427e19f6d0ddbb5ea1 100644
--- a/pkg/analyzer/lib/src/task/driver.dart
+++ b/pkg/analyzer/lib/src/task/driver.dart
@@ -25,6 +25,12 @@ class AnalysisDriver {
    */
   final TaskManager taskManager;
 
+//  /**
+//   * The list of [WorkManager] used to figure out which analysis results to
+//   * compute.
+//   */
+//  final List<WorkManager> workManagers;
+
   /**
    * The context in which analysis is to be performed.
    */
@@ -469,3 +475,24 @@ class WorkOrder implements Iterator<WorkItem> {
     return false;
   }
 }
+
+/**
+ * [AnalysisDriver] uses [WorkManager]s to select results to compute.
+ *
+ * They know specific of the targets and results they care about,
+ * so they can request analysis results in optimal order.
+ */
+abstract class WorkManager {
+  /**
+   * Return the next [TargetedResult] that this work manager wants to be
+   * computed, or `null` if this manager doesn't need any new results.
+   */
+  TargetedResult getNextResult();
+
+  /**
+   * Notifies the manager that the given [outputs] were produced for
+   * the given [target].
+   */
+  void resultsComputed(
+      AnalysisTarget target, Map<ResultDescriptor, dynamic> outputs);
+}