Don't schedule SOURCE_KIND computation when it is know already.

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

Index: pkg/analyzer/lib/src/task/dart_work_manager.dart
diff --git a/pkg/analyzer/lib/src/task/dart_work_manager.dart b/pkg/analyzer/lib/src/task/dart_work_manager.dart
index 3d6dc3375e1ee50ab55b63c6de1c55f1212a3d63..6b2a96ecc7c2a8344667bf150b9b92ab4159e2e2 100644
--- a/pkg/analyzer/lib/src/task/dart_work_manager.dart
+++ b/pkg/analyzer/lib/src/task/dart_work_manager.dart
@@ -117,7 +117,10 @@ class DartWorkManager implements WorkManager {
   void applyChange(List<Source> addedSources, List<Source> changedSources,
       List<Source> removedSources) {
     addedSources = addedSources.where(_isDartSource).toList();
-    changedSources = changedSources.where(_isDartSource).toList();
+    changedSources = changedSources
+        .where(_isDartSource)
+        .where((source) => _needsComputing(source, SOURCE_KIND))
+        .toList();
     removedSources = removedSources.where(_isDartSource).toList();
     // unknown queue
     unknownSourceQueue.addAll(addedSources);